Listen to a conversation between a student and a professor of her theater class.
Student:So, Professor Baker, about our next assignment you talked about in class.
Professor:Yes, this time you'll be in groups of three, each of you will have a chance to direct the other two in a short scene from a play you've chosen yourself.
Student:Right, and, well, I've been reading about story theater, and…
Professor:Ah, story theater, tell me about what you've read.
Student:Well, it's a form of theater where folk or fairy tales are acted out.It was…eh, introduced, by the director Paul Sills in the 1960s.In Sills's approach, an actor both narrates, and acts out a tale.So, like someone will appear on stage, and then will start narrating a tale, about…say a king, and then the same person will immediately switch to and start acting out the role of the king, with no props or scenery.
Professor:Sills, you know I actually saw his first story theater production in 1968, he did the fairy tale ‘the blue light'.
Student:Really, so whatever gave him the idea to produce that?
Professor:Well, as you know, back in the late 1960s, lots of people in the United States were disillusioned with the government.Sills was grappling with how to produce theater that was relevant in such times.Then he happened to read ‘the blue light', and he realized that it had just the message he wanted.
See, in the story, a man has lost all hope as a result of the unfortunate events in his life, completely turns his life around, with the help of a magical blue light. So,the blue light in the story symbolizes a way out of seemingly unsolvable human problems.And for Sills, that light symbolized an answer to the political turmoil in the US.
Student:But weren't you…um, audiences bother that the actors were performing on a bare stage?
Professor:Well, story theater is a departure from traditional dramatictheater with its realistic elaborate props and scenery, but Sills could make us see, say a big tall mountain through the facial expressions and body movements of the actors, and they're telling of the story.
We were all swept up, energized by such an innovative approach to theater, even if one or two of the critics weren't as enthusiastic.
Student:Cool, so, anyway.What I really wanted to ask, I'd love to try doing story theater for my project instead of just a scene from a traditional play.
Professor:Um, that's possible.A short tale can be about the same length as a single thing.Which fairy tale would you do?
Student:Actually, I was reading about another director of story theater, Rack Stevenson.You know, he produces plays based on folk tales as well.Maybe I could direct one of those.
Professor:Okay, yes, Rack Stevenson.Now, Stevenson's style's story theater is a little different from Sills's.He'll use simple props, a chair will represent a mountain, but the significant difference is with the narrator.The narrator will play only that role.Let's talk about why.
1.Why does the student go to see the professor?
A. To learn about the background of a director who was discussed in class
B. To ask permission to use a specific type of theater for her class assignment
C. To discuss the symbolism in a play she wants to use for her assignment
D. To find out what scenery she is allowed to use in presenting her assignment
2.Why does the professor discuss the political environment in the United States in the 1960s?
A. To compare events at that time to events that occurred in one of Stephenson’s plays
B. To suggest that the woman do additional research on that period of United States history
C. To point out why political themes are common in folk and fairy tales
D. To explain Sills's inspiration for his first story theatre production
3.According to the professor, what does the blue light in the fairy tale called "The Blue Light" represent?
A. A plan that is impossible to follow
B. A conflict between two opposing forces
C. A solution to complex problems
D. A question that has no clear answer
4.What is the professor's opinion about Sills's production of The Blue Light?
A. He thinks that it was an inventive and powerful performance.
B. He believes that the use of some props would have enhanced the performance.
C. He thinks that the theme is even more relevant today than it was in the 1960s.
D. He believes that it was less effective stylistically than some of Stephenson's plays.
5.According to the professor, what is the most important difference between Stephenson's and Sills's style of story theatre?
A. The actor who plays the role of the narrator plays only that role in Stephenson's productions.
B. The actors wear elaborate costumes in Stephenson's productions.
C. The stage settings are realistic in Stephenson's productions.
D. Political themes are avoided in Stephenson's productions.
托福TPO听力54原文+题目:Migration of Zooplankton浮游动物的迁移
Listen to part of the lecture in the marine biology class.
And the sea is teaming with tiny organisms, but they don't get as much popular attention as say, whales.
Microscopic algae just aren't as exciting I suppose.And yet those organisms are the foundation of the bulk of the marine food chain.Without plankton which is the global term for these tiny organisms, there will be no whales.
Plankton is found both in fresh water and marine environments.Again it's a term we use for any small organisms that float along with the current, either because they are too small or weak to swim against it, or because they don't have any capacity at all to move by themselves.
Plants and plant-like plankton are called phytoplankton while animals and animal-like plankton are called zooplankton.
For over a century now, researchers have been trying to solve the mystery about zooplankton.
You see some species of zooplankton migrate are……um…… not the way birds do when the seasons change.But daily, in the phenomenon we call Diel Vertical Migration or DVM, in the Diel Vertical Migration, sole plankton swim up near the surface of the water during the night and swim down to deeper water during the day.Depending on the species and region, this can be a round trip of between 100 and 400 meters.
For a tiny microscopic organism, that's a huge distance. Remember now, zooplankton can't swim very well and DVM requires a lot of energy.So there must be an important benefit to these daily up-and-down commuting.We're not exactly sure what this benefit is.Though there are several compelling theories.
I'll talk about them in a moment, but first I want to talk about what we do know or rather what we are pretty sure we know.
So researchers generally agree that the stimulus for zooplankton DVM is light.Zooplankton tend to swim away from sunlight into deeper water where the sun's rays barely penetrate.At night, when the sun no longer illuminates shallower water, zooplankton head back toward the surface.
Now why would light cause zooplankton to expend all that energy in migrate?
One popular theory is that zooplankton are hiding during the day from visual predators, eh……those animals that hunt by sight, the darkness provides safety during the day.
Then at night after migrating upward, they have an opportunity to feed on phytoplankton that float at the surface.Make sense, doesn't it?
But what do we do with the data showing that many kinds of zooplankton don't dive deep enough during the day to become invisible to predators or that others dive deeper than it's necessary to escape hunters' eyes.And some zooplankton are bioluminescent, which means they have special organs that ligh up and make them visible even at great depth.
Well, despite all these, we believe predator avoidance is a possible explanation because of studies done in fresh water lakes.It turns out there is a correlation between the presence or absence of vertical migration, and the presence or absence of fish that find their prey by sight.
But what are some other possible explanations?
Some researchers suggest that zooplankton migrate to avoid the sun's ultra-violet light.That would explain why some zooplankton are found at such great depth.Visible light may not penetrate very far down, but ultra-violet light can.And we know that some zooplankton have special pigments that protect them from the damage ultra-violet light can cause.
That could be why some zooplankton are able to stay closer to the surface during daylight hours.
And there is a third theory.
Although it takes a lot of energy for the zooplankton to migrate, they conserve energy while floating in deeper colder water.So while they're not feeding, they are quietly digesting in cooler water.
But remember, zooplankton consist of any number of different organisms.From microscopic worms to crab larvae to tiny fish, and they are found in a large range of marine habitats, cold water, warm water, shallow water, deep water.
So there may be different reasons for different species.
1.What does the professor mainly discuss?
A. The importance of zooplankton in the marine food chain
B. The interdependence of two types of tiny marine organisms
C. A physical feature of zooplankton that makes them well adapted for swimming
D. A phenomenon observed in some species of zooplankton
2.Why does the professor conclude that zooplankton must derive an important benefit from diel vertical migration?
A. Diel vertical migration uses up a lot of energy.
B. Diel vertical migration exposes zooplankton to predators.
C. Diel vertical migration prevents zooplankton from being able to digest phytoplankton.
D. Diel vertical migration forces zooplankton populations to live permanently in cold water.
3.What does the professor imply about bioluminescent zooplankton?
A. Their food source is different from that of other zooplankton.
B. They probably do not rely on diel vertical migration to avoid predation.
C. They migrate deeper than other zooplankton species do.
D. Most species are found in very cold water.
4.Why does the professor mention fish that live in freshwater lakes?
A. To point out that many aquatic species exhibit diel vertical migration
B. To give an example of a species of fish that feeds on bioluminescent zooplankton
C. To make a comparison between fish and zooplankton
D. To support one of the theories explaining why zooplankton migrate
5.Avoiding predators is one possible explanation for why zooplankton dive so deeply in the ocean. What two other explanations for this phenomenon does the professor offer?Click on 2 answers
A. To avoid ultraviolet light
B. To avoid strong ocean currents
C. To digest in colder waters
D. To find abundant food sources
6.What does the professor imply about the reasons for diel vertical migration in zooplankton?
A. No single explanation for all species can account for this phenomenon.
B. Researchers have not been able to propose plausible theories to explain this phenomenon.
C. All individual organisms have several reasons for migrating.
D. Researchers were able to agree on an explanation for this phenomenon after many years of investigation.
托福TPO听力54原文:Benefits of Muon Detectors介子探测器的好处
Listen to part of a lecture in an archaeology class.
Professor: A popular misconception about archaeology, some people imagine we just go out into the field with a shovel and start digging, hoping to find something significant.
Well, while there is an element of luck involved, we have an array of high-tech tools to help us figure out where to concentrate our efforts.
One of the newer tools actually relies on particle physics, talk about inter-disciplinary.
Here is a machine that brings together two very different sciences.This machine is called a muon detector.
Muons are subatomic particles that result from cosmic rays.
OK, let me start over.Cosmic rays aren't actually rays.They are basically protons zipping through outer space at close to light speed.And, when they collide with the atoms in earth's atmosphere, they break up into smaller particles -- muons.
Now these muons are still highly energized, so they can easily pass on down to the earth's surface.In fact, they can pass through solid matter, so they can also penetrate deep into the surface.And it's this property of muons that archaeologists are taking advantage of.
Let me explain, with the right kind of equipment, scientists can use muons to create a kind of picture of the structures they are studying.
Let's say we are studying a Mayan pyramid in central America.And we are interested in finding out if there are burial chambers or other rooms inside.Well, a muon detector will show a greater number of muons passing through the less dense areas inside the pyramid.
Andrew: Um…I'm not sure I get how this muon detector works exactly.
Professor: Well, muons lose energy as they pass through dense material, like the stone walls of the Mayan pyramid.So more muons and more energetic muons will be passing through empty spaces.The muon detector can differentiate the areas where more muons are passing through -- the empty spaces, as well as where there are fewer muons, the walls and dense areas.
These empty spaces will show up as darker, so we wind up with a kind of picture of the pyramid, and its internal structure.
Andrew: A picture?
Professor: Sort of like an X-ray image.
Andrew: Ok, so if we see darker areas inside the pyramid, we assume it's an empty space with more muons.
Professor: Exactly, with this technology, we can see what's inside the structure before we dig, so we know exactly where to explore and we can minimize the damage excavation can cause.
Even a little damage could result in us losing vital information forever.
Now, muon detectors have been around for some time, but they have been improved upon since archaeologists started using them.
In 1967 a physicist placed a muon detector beneath the base of one of the Egyptian pyramids of Giza.And he was looking for burial chambers.Now it happened that the muon detector found none.But he did demonstrate that the technique worked.
Unfortunately the machine he used was so big that many archaeologists doubted muon detection could be practical.How could they get a massive piece of equipment into, say, the jungle of Belize?
Then there was the issue of range.
The machine used in 1967 could only scan for muons directly above it, not from the sides.So it actually had to be put underneath the pyramid, so it could look up.That meant if you wanted to find out what was inside an ancient structure, you first had to bury the detector beneath it.
There's been a lot of work on these machines since then.And these problems have been solved by and large.That's not to say the technology is perfect, it would be nice for example, to have a system that didn't take 6 months to produce an image.I suppose that's better than the year it took for the 1967 study to get results.
But still...well, there is good reason to believe that with better equipment, we're going to see muon detectors used much more frequently.They are already being used in other areas of science, for example Japanese scientists studying the interior of volcanoes, and there are plenty of archaeologists who would love to use this technology.
1.What is the lecture mainly about?
A. Misconceptions about muon detectors
B. An investigation of an Egyptian pyramid using a muon detector
C. The collaboration between physicists and archaeologists in the development of the muon detector
D. Benefits that muon detectors can provide to archaeologists
2.What aspect of muons is most useful to archaeologists?
A. Their ability to carry information from outer space
B. Their ability to break down cosmic rays into smaller particles
C. Their ability to pass through solid matter
D. Their ability to change the color of some surfaces
3.According to the professor, what information can a muon detector provide about an ancient structure?
A. The internal temperature of the structure
B. The location of rooms within the structure
C. The age of the structure
D. The materials used to build the structure
4.Why does the professor discuss damage to archaeological sites?
A. To indicate a benefit of using muon detectors in archaeological research
B. To describe an accident with a muon detector during a pyramid excavation
C. To explain how muon detectors are useful in reconstructing damaged sites
D. To explain why muon detectors were not often used in the past
5.In what ways are modern muon detectors different from muon detectors used in 1967?Click on 3 answers
A. Modern detectors are less expensive.
B. Modern detectors use less energy.
C. Modern detectors are not as large.
D. Modern detectors take less time to produce an image.
E. Modern detectors can scan in more than one direction.
6.What is the professor's opinion about the newer muon detectors?
A. She appreciates the help they provide despite the time they take to produce images.
B. She fears that many archaeologists will be unwilling to learn to use them.
C. She feels that they have greater potential in areas of science other than archaeology.
D. They provide more accurate information about the age of objects than older detectors did.
托福TPO听力54原文+题目:Finding Historical Material寻找历史材料
Listen to a conversation between a student and an employee in the university's historical library.
Employee: Morning, what can I help you find?
Student: Well, I saw the internet that the university library has menus and things from local restaurants, like the Springfield Eatery?
Employee: Right, a lot of local businesses have donated materials to our collection, including that restaurant.I'm pretty sure we have ten or fifteen boxes of materials from there.
Student: Good, I thought you were located in the main library, so I went there first and they sent me here.I haven't realized the university has a separate historical library.I think what you're doing is great，collecting local documents and photos, keeping a record of the region.
Employee: I'm glad you see the value of it.We've been collecting materials for going on seventy years now.Last year we had an exhibition that showcase how the town square has changed over the past fifty years.
So, that got the word out a little, but you're right.A lot of students don't know we exist.Well, unless the major of new history.So, you're looking for something for class?
Student: Not exactly.My grandmother went to this university, and while she was here, she worked as a waitress.
Employee: At the Springfield Eatery?
Student: Yes, and that's where she met my grandfather.So, they're celebrating their fiftieth anniversary this year.And I noticed online that you have old menus from some of the restaurants.I was thinking I could find one from the year they met and print a copy for them.
Employee: What a unique idea!What year you are looking for?
Student: Um, 1954.
Employee: I know we have a few menus from the 1950s, but you'll have to check.There are some gaps, some years we didn't receive any new materials, and sometimes restaurants go a while without changing their menus.
Student: Oh no, I really want to give them something special.
Employee: Well, how about this? We also have a lot of photos, so maybe you could find one of your grandmother, or maybe even one with both your grandparents.
Student: That would be awesome.
Employee: The only thing is most of our materials are still in boxes.No one's ever taken the time to organize them.So, it …it might require a fair amount of sifting.
Student: Um, I have a couple of tests coming up, but I can take a quick look, if that's okay.I know some libraries have special rules for handling delicate or old materials.
Employee: Well, these aren't particularly old.Just the usual rules apply, no food or drinks.
Student: Okay, thanks for your help.
1.Why does the man go to see the woman?
A. To ask the woman if she has photographs of local businesses
B. To conduct research for a history class
C. To try to find a gift for his grandparents
D. To find out how long a local restaurant has been in business
2.What does the woman say about an exhibition the library held last year
A. It was in honor of the town's seventieth anniversary.
B. It helped increase awareness of the collection.
C. It was arranged by students who study history.
D. It mostly included photographs from the 1950s.
3.What does the woman imply about the menus?
A. Most of the menus in the collection are from the Springfield Eatery.
B. All of the menus in the collection are carefully organized in boxes.
C. The menu the man is looking for is probably in the main library.
D. The man might not find the menu he is looking for.
4.What does the woman suggest that the man consider doing?
A. Look for a photo of his grandparents
B. Frame a photograph of a menu from a different year
C. Call the restaurant to ask whether they have what he is looking for
D. Take a picture of the restaurant
5.Why does the man say this:
A. To inform the woman that he has handled old materials in the past
B. To inquire whether the library has regulations for handling historical documents
C. To imply that the library should do a better job protecting historical documents
D. To argue that special precautions are not necessary in this case
托福TPO听力54原文+题目:William Wheatley and Broadway Theaters威廉?惠特利和百老汇
Listen to part of a lecture in a theater history class.
One of the things New York city is known for is its Broadway theaters，the productions of elaborate musicals.A lot of money goes into producing a musical with the actors, costumes, scenery and so on.The shows are designed to appeal to large audiences, to make the production financially viable.But theater didn’t always appeal to the masses.In the middle of the 19th century, with mostly wealthy residents who were going to Broadway, they would see an opera that was probably written and produced in Europe before making its way all over to New York.It was a scene for, well, the socially prominent, the upper class, who attended these functions, perhaps, because they felt obligated rather than because of a genuine interesting theater.
But, in the 1860s, something else started to occur.The middle-class population began to grow, and they were looking for a source of entertainment.Keep that in mind while I talk about the theater owner named William Wigley.In 1866, Willian Wigley had this show, um, and it was different from most shows on Broadway at the time because it wasn’t an opera.And, it was developed right here in the United States, in English, unlike the operas which were typically Italian or French.Wigley also decided to incorporate some fancy production techniques, stage effects.The show also included music to make it more entertaining.And, through a stroke of luck, a world-renown ballet troop became available just as weekly show was about to open.So, he didn’t hesitate to include the ballet dancers in his production.Along the lines of those special affects I mentioned, Wigley redesign the entire stage for the show.Every floor board on the stage could be lifted up or pushed down.They were all moveable.This allowed for trap doors to be placed anywhere on the stage.So, pieces of the set, of the scenery, could easily be stored beneath the stage.And these trap doors also gave performers another less traditional way to enter in exit of the stage.Well, today, we might not think much of it, things like this are standard nowadays，the concept was quite novel at the time of Wigley show.And was one of the things that made the show a hit with audiences.
Another innovative element in the show was a scene called the ‘transformation scene’, during this scene, the audience watched in amazement that a setting on stage changed from a moonlit cave to a throne room in a palace.Normally to have this type of major scene change, the curtains were closed, the stage crew would remove the previous set and replaced it with the new one, and then, the curtains would open again.In this instance though, the transformation to place in front of the audience using simple machinery.And this affect would have the lasting impression on everyone who saw Wigley’s production.
In fact, those people were probably disappointed when they saw another show that didn’t contain something is, well, as elaborate or exciting.So, look, when it premiered, Wigley show took audiences by surprise, it appealed to large crowds including the growing middle-class, the show ran for almost two years straight in New York city, and achievement unheard of at the time when productions typically lasted weeks or months, not years.It also went on tour visiting different cities across the United States for over 25 years.So, the show was quite a success.
And with all that in mind, some people call Wigley show the first musical on Broadway.Now our current definition of a musical is that it tells a story through dialogue and song.In Wigley show the musical sections, well, they didn’t necessarily integrate well with the story.Giving an overall impression of something more like a variety show, yes, everything was loosely focused around the central scene, so maybe it’s fair to say then that the show gave audiences a hint of a new form of musical theater， that would ultimately appear on Broadway in the decades to follow.
1.What is the main purpose of the lecture?
A. To describe the influence of opera on Broadway productions
B. To explain how new technology allowed for enhancements to Broadway productions
C. To evaluate financial decisions made by theater owner William Wheatley
D. To examine elements that set a particular theatrical production apart from earlier ones
2.What was typical of theatrical productions in the United States before the 1860s?Click on 2 answers
A. The productions originated outside of the United States.
B. Only a limited segment of society attended the productions.
C. People attended the productions because they were interested in the plots.
D. The themes of the productions were typically related to the upper class
3.According to the professor, what was a reason for a change in theatrical productions in the United States during the 1860s?
A. A growing middle class was in need of entertainment.
B. Wealthy theater advocates provided additional funding for new productions.
C. The interest of theatergoers shifted from opera to ballet.
D. A new artistic movement was founded by a group of actors
4.Why does the professor mention moveable floorboards on the stage in Wheatley's production?
A. To explain the reason for an unexpected technical problem
B. To highlight one of the production’s innovative features
C. To point out a similarity between early and modern theater in the United States
D. To give an example of a modification that was made for the ballet troupe
5.What was the audience's reaction to the transformation scene in Wheatley's production?
A. The audience was disappointed by the scene's short duration.
B. The audience was confused by the scene's unfamiliar elements.
C. The audience was amazed by the scene-changing process.
D. The audience was impressed at how quickly the stage crew moved objects onto the set
6.According to the professor, what is one way in which Wheatley's production was different from modern musicals?
A. The performers in Wheatley's production performed more than one role.
B. Wheatley's production was created for the upper class.
C. The songs in Wheatley's production did not include lyrics.
D. The musical numbers in Wheatley's production did not correspond with the plot
托福TPO听力54原文+题目:河流猜想的新证据_New Evidence of River Hypothesis
Listen to part of a lecture in a geology class.
Professor: About 30 years ago, a geologist named Edward Cotter, that's C-O-T-T-E-R, published a paper that contained a very interesting hypothesis.
He was studying ancient rivers in the North American mountain chain.And he noticed that about 450 million years ago, rivers started to behave differently.Before then, rivers were wide, shallow and straight.But after that time, they became deeper and had more curves.They became increasingly meandering, and that's actually how rivers behaved till this day.
So why might this change have happened?
Student:Maybe there was some kind of a climate shift?
Professor:Well,lots of climate shifts have happened since then.
Student:Was the change worldwide? Or just in that geographical area?
Professor:Well Cotter speculated that rivers changed worldwide, but he couldn't prove it.Because he only had evidence from the one North American mountain chain.But his studies gave him an idea about why rivers started to change.He hypothesized it had to do with the spread of plant life on earth.
Student: So there was no plant life before 450 million years ago?
Professor: Very little according to fossil records.Anyway, geologists were intrigued by this hypothesis which claims that as plants evolved and spread, they had an effect on terrain and rivers.In the past 30 years, more studies have been done.And now we have a lot of data about river systems from around 450 million years ago from all over the world.
In a recent study, a couple of researchers gathered together the existing data and combine them with their own new field data to get a comprehensive picture of the situation.
Their study was specifically designed to identify changes in the shapes of rivers during the time period when vegetation was evolving.
And when the researchers compared the data about river shapes with data they have collected about plant life from the same period, the data seemed to prove Cotter's hypothesis.
Student: OK, but how did plant life affect rivers?
Professor: Well, in order to answer that question, we need to look at the geological evidence.
You see, as rivers flow, they leave layers of sediment behind that eventually fossilized.The content, thickness and shape of these fossilized layers and rocks gave us information about how rivers flowed.The earliest records from 500 million years ago show that the sediment in river deposits was largely composed of quartz grain of sand and gravel.That tells us that rivers weren't defined, they were very shallow and wide, almost like floods.
But around the time of the rise of plant life, the content of those sediment layers began to change.The quartz grains became much finer.And we see evidence of mud.This suggests that plants promoted the preservation of mud when they sent their roots into the ground.The roots helped to reinforce the ground, which in turn allowed for the creation of river banks.
And we also see evidence of a process called lateral accretion.
Lateral accretion happens when water flows around the curve or bend in the riverbed.Now the speed of the flow on the outside of the bend is fastest, and slowest on the inside of the bend.This sets up what's called the secondary flow across the river bottom.The fast flowing water on the outside of the bend digs out material from the riverbank and pushes these material laterally across the bottom, and it gets deposited on the other side of the river,on the inner side of the bend.
So, when we see in the sediment layers, evidence of lateral accretion, the erosion on one side and deposits on the other, that's an indicator that meandering rivers existed.
And according to the study, strong evidence of lateral accretion appears in the geological record.At the same time, there is also evidence of plants with underground root systems.This suggests that plants promoted the development of modern rivers by creating stable banks, which resulted in the flow of water in single meandering channels.
Student:So it looks like the researchers were able to prove that hypothesis.
Professor: Well, there is no denying that this study presents a very strong case.But some questions about this hypothesis remain.For example, it's well-known that on other planets, like Mars, there is clear evidence of meandering rivers.But is there evidence of vegetation on Mars? I think not.
1.What does the professor mainly discuss?
A. A hypothesis that rivers formed before the rise of plant life
B. A study of the effects that rivers have on soil formation
C. A debate surrounding two opposing hypotheses
D. New evidence in support of a previously proposed hypothesis
2.What limitation of Cotter's research does the professor mention?
A. Cotter's research findings could not be replicated.
B. Cotter's research was based on one geographical area.
C. Cotter's research did not take into account lateral accretion.
D. Cotter's research did not account for changes in climate.
3.What did researchers try to confirm about rivers in a recent study?
A. That rivers now have the same shape worldwide
B. That rivers were responsible for the spread of plant life
C. That a change in the shape of rivers is linked to the spread of plant life
D. That most rivers emerged during a specific geological time period
4.Why does the professor describe the composition of the sediment of the earliest rivers?
A. To identify the evidence used to determine how the rivers flowed
B. To explain why the rivers could easily dry out
C. To suggest that the sediment was once fine sand
D. To suggest that the geological record might be flawed
5.According to the professor, what is an effect of lateral accretion on a meandering river?
A. Bends in the river become gradually straighter.
B. Material from one riverbank is deposited on the other.
C. The intensity of the river's flow increases.
D. The growth of plants on the outer riverbank is enhanced.
6.Why does the professor say this:
A. To find out what the students know about Mars
B. To question certain geological studies of other planets
C. To express a reservation he has about the hypothesis
D. To indicate that he is going to change the topic