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  3. Since there is such an abundance of food in the sea, it is understandable that some of the efficient, highly adaptable, warm-blo

Since there is such an abundance of food in the sea, it is understandable that some of the efficient, highly adaptable, warm-blo

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问题     Since there is such an abundance of food in the sea, it is understandable that some of the efficient, highly adaptable, warm-blooded mammals that evolved on land should have returned to the sea. Those that did do that have flourished. Within about 50 million years—no time at all, geologically speaking —one of the four kinds of mammals that has returned to a marine environment has developed into the largest of all animal forms, the whale. A second kind, the seal, has produced what is probably the greatest population of large carnivorous mammals on Earth. This suggests that these "top dogs" of the ocean are prospering and multiplying. However, such has not been the case, at least not for the last 150 years. Trouble has closed in on these mammals in the form of equally warm-blooded and even more efficient and adaptable predators, humans. At sea, as on land, humans have now positioned themselves on top of the whole great pyramid of life, and they have caused serious problems for the mammals of the sea.
    There is a simple reason for this. Marine mammals have the misfortune to be swimming aggregates of commodities that humans want: fur, oil, and meat. Even so, they might not be so vulnerable to human depredation if they did not, like humans, reproduce so slowly. Every year humans take more than 50 million tons of fish from the oceans without critically depleting the population of any species. But the slow-breeding mammals of the sea have been all but wiped out by humans seeking to satisfy their wants and whims.
It can be inferred from the passage that during the last 150 years humans have ______.
选项 A、constructed submarines
B、learned how to swim
C、threatened the existence of some marine mammals
D、begun to harvest certain plants from the ocean as food
答案C
解析 根据文章第一段最后四句可知，这些海洋中的“大哥大”们人丁兴旺，一派繁荣景象。但事实并非如此，至少在过去150年来是这样。同样是暖血动物而且效率更高、适应性更强的捕食者——人类，已成为这些哺乳动物日益迫近的威胁。和在陆地一样，人类在海洋也已处在巨大的生物金字塔的最顶端，成为所有生物的主宰，给海洋哺乳动物带来严重威胁。据此判断，答案是C。
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