2. 外语
  3. Many people feel that human beings should be responsible for the disappearance of some other animal species. It is true we may【M

Many people feel that human beings should be responsible for the disappearance of some other animal species. It is true we may【M

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问题     Many people feel that human beings should be responsible for
the disappearance of some other animal species. It is true we may【M1】______
have hastened the disappearance of some species, but abundant
evidence suggests that mankind has actually had few impact Biologists【M2】______
point out that 50 species can be expected to disappear in the 20th
century but also remind us that about 50 species became extinct in the
19th century, and 50 species in each of the centuries after that Dr. T. H.【M3】______
Jukes at the University of California has pointed out that about 100
million animal species have become extinct since life began on the
earth about 3 billion years before. Thus, animals come and animals【M4】______
go as a consequence of natural selection as Mr. Darwin had invented.【M5】______
The human race is a recent newcomer to the scene, so we’ve had
nothing whatsoever to do with the disappearance of millions of species.
    In fact, when it comes right down it, we’re a miserable failure【M6】______
at genocide. In spite of an all-out centuries-old war against rats, but【M7】______
we haven’t made a dent in its numbers, much less extinguished a【M8】______
single species. And in spite of all our high technology we have not
been successful on eliminating a single undesirable insect species!【M9】______
    I’ve come to the conclusion that the people who are trying to
save world are probably quite sincere about it, therefore they don’t know【M10】______
much about science and certainly nothing about systems engineering.
【M4】
选项
答案before→ago
解析 词汇错误。before和ago都表示“以前”，但before主要用于过去完成时，ago主要用于一般过去时。since引导的从句用的是一般过去时(began)，所以要把before替换成ago。
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