2021年8月28日托福阅读真题+题目+答案：Causes of Amphibian Declines

2021年8月28日托福阅读真题+题目+答案：Causes of Amphibian Declines

A striking feature of amphibian population declines, and what sets them apart from the general biodiversity crisis, is that they have occurred in some of the best-protected natural areas. For example, Sierra Nevada Yellow-legged Frogs have disappeared from wilderness areas high in the United States mountain range known as the Sierra Nevada. While remote locations such as these have escaped obvious habitat alteration and destruction, they are still being affected by human activities. Scientists have investigated five possible causes for the mysterious rapid amphibian declines that have occurred in such remote locations: (1) introduced nonnative species, (2) increased ultraviolet radiation, (3) disease, (4) climate change. and (5) toxic contaminants such as pesticides.

1.According to paragraph 1, what makes the declines in amphibian populations different from the general biodiversity crisis?

O They are not due to human activities.

O There are clear ways to protect against them.

O They have been happening more rapidly than other effects of the crisis.

O They happen even in places where the habitat remains unchanged.

2.Which of the following can be inferred about the Sierra Nevada from paragraph 1?

O Because of its climate, it has few amphibians

O Scientists have studied few of its frog habitats.

O It is one of the sites most affected by the general biodiversity crisis.

O Humans have not caused extensive changes to its habitats.

People introduce nonnative species for a variety of reasons, including for recreational fishing, for human food, and for biological control of pests. For example, as early as the 1800s, fish stocking of high-elevation lakes in the Sierra Nevada was done by horseback. ⬛ Today, trout are raised in hatcheries and dropped by airplane into remote sites in mountain ranges throughout the West. ⬛ Trout are heavy predators and will eat both tadpoles and adult frogs, so they could easily be the cause behind some declines. ⬛ While introduced species such as trout have significant negative impacts on certain amphibian species, scientists are concluding that they are not the predominant cause of rapid declines. ⬛

3.The word "predominant" in the passage is closest in meaning to

O main

O only

O reported

O current

Increased ultraviolet radiation was long thought to play a role in declines, and it has received much scientific attention. The release of ozone-destroying chemicals such as chlorofluorocarbons (CFCs), formerly used in refrigerators, has resulted in increased ultraviolet radiation reaching Earth's surface. Ultraviolet radiation can cause DNA damage and affect animal immune systems. However. the largest number of rapid declines has occurred in tropical mountain-slope forests where amphibians are sheltered from sunlight by the forest canopy. Thus, ultraviolet radiation is unlikely to be a primary cause of these declines.

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