Question 20 is based on the passage you have just heard.

听力原文

    (19) [An endangered species of whale is experiencing a small baby boom off the coast of America.] The North Atlantic right whale is one of the rarest species of whale on the planet, numbering only about 411. But the Center for Coastal Studies said Friday that its aerial survey team spotted a mum with two babies in Cape Cod Bay a day earlier. That brings the number seen in nearby waters alone this year to three. That’s big news because the whale population has been falling, and no baby whales were seen last year. In all, seven baby whales have been spotted so far this year. (20) [The whale population has become endangered due to commercial whaling activities in recent years.] This is because they are sometimes hunted for their meat or their skin. Over-hunting could lead to the disappearance of the whale population, possibly causing major problems to the global food chain. (21) [The whales give birth off the southeast coast of America in the winter and travel to feeding grounds off the northeast coast in the early spring.] The northeast coast is a critically important source of food. The animals often feed close to shore. This provides watchers on land with “unbeatable views of one of the rarest of marine mammals.” It’s illegal to get within 1,500 feet of the animals without a federal research permit, so whale watchers are discouraged from attempting to get close to the whales.

20. What has caused the decline of the whale population in recent years?（近年来，是什么导致了鲸鱼数量的减少？）

解析：C。此题可用到视听一致和同义替换。录音中提到，由于近年来的商业捕鲸活动，鲸鱼（北大西洋露脊鲸）的数量已经濒临灭绝。因此C项符合题意，Commercial hunting是对录音中commercial whaling activities的同义替换，为正确答案。

错项排除：录音中没有提到全球变暖或海水污染的问题，排除A和B项。录音开头说到，一种濒临灭绝的鲸鱼（北大西洋露脊鲸）正在美国海岸附近经历一次小规模的生育潮，可知鲸鱼并非由于出生率下降而濒临灭绝，D项错误。