托福模拟试题听力 - TPO20 - 讲座4

时间 : 2013-08-15 08:27来源 : VOA官网 收听下载次数 :
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TPO20 Lecture4 Biology  

Professor:Now, James, you said you had been to the State of Maine, right?

Student:Yeah, actually I lived in western Maine until I was about sixteen.

Professor:Great. So why don’t you tell everybody what is like there in the winter?

Student:The winter? Well, it’s cold. And there’s lots of snow, you wouldn’t believe how much snow we used to get.

Professor:Actually I would. I did field research up there a couple of winters. And it really is an incredible environment. And to survive in that sort of environment, animals have to adapt, to evolve in response to their surroundings. As you recall, an adaptation is any feature, um... physical or behavioral feature of a species that helps it survive and reproduce. And in adapting to extreme climates, like Maine in the winter time, animals can evolve in pretty interesting ways. Take, for example, the snowshoe hare. Ok, the snowshoe hare, and of course, that’s H-A-R-E, like a rabbit. Although I probably should mention that technically a hare is not exactly the same as a rabbit, even though it is very similar . The primary difference is that a rabbit’s young are born blind and without fur , while a hare’s babies are born with a full coat and able to see. Now, the snowshoe hare, tell me, what sort of adaptations do you think it has developed that help it survive the Maine winters? I’ll give you a hint. Food isn’t an issue. The hare actually has abundant food in the small twigs it finds.
  
Student:
Well, I don’t know. I mean, I know we used to try to look for these rabbits, eh... hares, when we went hiking in the winter , but it was often hard to find them in the snow.

Professor:Yes. That’s exactly right. The major concern of the snowshoe hare in the winter is predators. And now that includes humans. So one of its adaptations is basically camouflage. In other words, its coat, its fur , turns from brown in the summer to white in the winter , which makes it harder for the hare’s predators to see it against the white snow.

Student:Yeah, but I could swear I remembered seeing rabbits in the snow a couple of times, I means hares, that were brown.

Professor:Well, you may very well have. Timing is really important, but the snowshoe hare doesn’t always get it exactly right. Its chances for survival are best if it turns white about the time of the first snowfall. And it’s the amount of daylight that triggers the changing of the hare’s coat. As the days get shorter , that is, as the Sun is up for a shorter and shorter time each day, the snowshoe hare starts growing white fur and shedding its brown fur . The hare does a pretty good job with its timing, but sometimes when there’s a really early or late snow, it stands out. Plus, it takes about a month for the snowshoe hare’s coat to completely change color . So if there’s a particularly early snowfall, it’s very likely that the hare’s fur would not yet be totally white. And that would make this a particularly dangerous time for the hare. OK. What else? Other adaptations? Susan?

Student:Well, it’s called the snowshoe hare, so are its feet somehow protect it from the cold?

Professor:Well, this animal’s name does have to do with an adaptation of its feet. Uh... though, not like it has warm furry boots or something to keep its feet from getting cold. You’ve probably never needed to wear snowshoes. But, well, snowshoes are not like thick furry shoes designed to keep the feet warm, they are actually quite thin, but very wide. What they do is spread out the weight of the foot coming down on the snow. See, the problem with walking on snow is that you sink in with every step. But with snowshoes, you don’t sink in, you walk on top of the snow. It makes walking through the Maine countryside in the winter much easier . Anyway, the snowshoe hare has an adaptation that plays on the same idea. It has hind feet that act like snowshoes. I mean, it’s paws are wide and they allow the hare to hop and run just at the surface of deep snow. And this is a huge advantage for the snowshoe hare since by contrast, the feet of its predators usually sink right down into the snow. Now, another advantage related to this is that unlike many animals in winter, snowshoe hares can stay lean6 and light weight. They accumulate essentially no body fat. Can anyone guess why this is so?

Student:They don’t eat very much?

Professor:Well, yes. But not because there isn’t enough food around. It’s because, like I said, food is almost always within reach, and they don’t have to store up a lot of food energy for the harsh winters.

 

1 What is the lecture mainly about?

A. Typical features of the snowshoe hare that do not result from adaptation

B. Various strategies used by snowshoe hares to find food during the winter

C. Characteristics that snowshoe hares have developed in response to their environment

D. Interactions between snowshoe hares and human populations in the state of Maine

 

2 According to the professor, what causes the snowshoe hare’s fur to begin turning white?

A. A decrease in the hours that the Sun is up each day

B. A sudden drop in temperature

C. The increasing amount of snow on the ground

D. The changing nature of the food supply

 

3  Why might an early snowfall be a particularly dangerous time for the snowshoe hare?

A. Its feet would not yet have grown to resemble snowshoes.

B. Its babies would not yet be able to keep themselves warm.

C. Its chances of being seen by a predator are much higher.

D. It might not be able to locate where it stored its food supply. 


 
4  The professor implies that the snowshoe hare has an advantage over other animals because of its unusual feet. What is that advantage?

A. It can reach food in higher locations better than its competitors.

B. It can stay warm in cold weather longer than its competitors.

C. It can outrun its predators in deep snow.

D. It can dig under the snow to hide from its predators.

 

5 The professor explains that the snowshoe hare’s food supply is available year-round. What does the availability of food allow the snowshoe hare to do?
A. Store body fat for the cold months

B. Remain lightweight through the winter

C. Give birth during the winter

D. Grow fur quickly during the first year after birth