2019年9月21日托福阅读真题+题目+答案：When the Wolves Returned

2019年9月21日托福阅读真题+题目+答案：When the Wolves Returned

One of the most fascinating discoveries in modern ecology is an abundance of trophic cascades. To understand what a trophic cascade is, one needs to understand the concept of a food chain. A food chain refers to a group of organisms of varying sizes that are related to one another in their predatory feeding, with smaller organisms being eaten by larger ones, which are, in turn, preyed upon by even larger ones, thereby creating a feeding chain, A trophic cascade occurs when the animals at the top of the food chain—the top predators—change the numbers not just of their prey but also of species with which they have no direct connection. Their impacts cascade down the food chain, in some cases radically changing the ecosystem, the landscape, and even the chemical composition of the soil and the atmosphere. The best-known example is the dramatic change that followed the reintroduction of wolves to Yellowstone National Park in the United States. Seventy years after they had been exterminated, wolves were released into the park in 1995. When they arrived, many of the streamsides and riversides were almost bare, closely cropped by the high population of red deer. But as soon as the wolves arrived, this began to change. It was not just that they sharply reduced the number of deer, but they also altered their prey's behavior. The deer avoided the places—particularly the valleys and gorges—where they could be caught most easily. In some places, trees on the riverbanks, until then constantly suppressed by deer eating there, quintupled in height in just six years. The trees shaded and cooled the water and provided cover for fish and other animals, changing the wildlife community that lived there. More seedlings and saplings survived. The bare valleys began reverting to aspen, willow, and cottonwood forest with the apparent result that the number of songbirds increased: among the resurgent trees a study has found higher populations of species such as the song sparrow, warbling vireo: yellow warbler and willow flycatcher.

The regrowth of the bankside forests in Yellowstone also appears to have allowed the animal populations of both beavers and bison to expand: beaver colonies rose from one to twelve between 1996 and 2009. The beavers then triggered other effects, creating places for otters, muskrats, fish, frogs，and reptiles. The returning trees have also stabilized the banks of the streams, reducing the rate of erosion and the movement of channels, narrowing the width of the streams and creating a greater diversity of pools and quick-running shallows. Similar effects have been recorded in Zion National Park in Utah: where cougars (large cats) are abundant 。。。。。余下托福阅读真题省略！

1.The word "radically" in the passage is closest in meaning to

A rapidly 

B gradually 

C permanently 

D drastically

2.According to paragraph 1, all of the following changes occurred in Yellowstone National Park after wolves were reintroduced EXCEPT:

A Deer started avoiding places where they could be easily caught. 

B Deer began feeding on trees on the riverbanks.

C Trees returned to the valleys.

D Some populations of songbirds increased.

3.Why does the author contrast the “hillsides in Yellowstone” with the "grasslands where the deer and pronghorn antelope grazed"?

A To imply that plant life in Yellowstone grasslands may eventually die off while it continues to flourish on the hillsides

B To illustrate how some areas of Yellowstone have remained unaffected by the return of the wolves

C To point out how varied the effect on soil and subsequent vegetation has been because of the change in deer populations

D To suggest that for at least some areas of Yellowstone: the reintroduction of wolves may have caused more harm than good

。。。。。余下托福阅读真题题目省略！

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