托福听力真题原文+题目+答案+mp3下载：meandering rivers

托福听力真题原文+题目+答案+mp3下载：meandering rivers

听力原文如下：

Narrator: Listen to part of a lecture in a geology class

Teacher: About 30 years ago, a geologist named Edward Cotter (that's C-0-T-T-E-R), published a paper that contained a very interesting hypothesis. He was studying ancient rivers in a 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 behave to this day. So, w h y might this change have happened?

Student: Maybe there was some kind of climate shift?

Teacher: Well, lots of climate shifts have happened since then.

Student: Was the change world wide, or just in that geographical area?

Teacher: Well, Cotter speculated that rivers changed worldwide. But he couldn't prove it, because he only had evidence from tlu one North American mountain chain. But his studies give 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?

Teacher: Very little according to fossil rlcords. Any way, geologists were intrigued by this hypothesis which claimed that as plant evolved and spread,they had an affect on the 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 combined them with their。。。。。余下听力原文省略！

听力真题题目如下：

1.What does the professor mainly discuss

A、Ahypothesis 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 1atera accretion.

D、Cotter's research did not account for changes in dlimate.

。。。。。余下听力真题题目及答案省略！

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