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【C1】______on land should have returned to the sea. Those that【C2】______have flourished. Within about 50 million years--【C3】______time at all, geologically speaking--one of the four kinds of mammals that has【C4】______to a marine environment has developed into the largest of all animal【C5】______, 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【C6】______and multiplying.【C7】______, such has not been the case, at ieast not for the last 150 years. Trouble has closed in【C8】______these mammals in the form. of equally warm-blooded and even more【C9】______adaptable predators, humans. At sea,【C10】______on land, humans have now【C11】______themselves on the top of the whole great pyramid of life, and【C12】______have caused serious problems for the mammals of the sea, There is a simple【C13】______for this.

【C14】______mammals have the misfortune to be swimming aggregates of【C15】______that humans want: fur, oil and meat. Even so, they might not be so【C16】______to human depredation if they did not, like humans,【C17】______so slowly.

Every year humans【C18】______more than 50 million tons of fish from the oceans without critically depleting the population of any【C19】______. But the slowbreeding mammals of the sea have been all but wiped out by humans【C20】______satisfy their wants and whims.

【C1】

A．involved

B．evolved

C．evoked

D．exceeded