2. 职称英语
  3. Once common throughout the Western plains, black-footed ferrets are thought to h

Once common throughout the Western plains, black-footed ferrets are thought to h

游客2024-01-13  96
问题 Once common throughout the Western plains, black-footed ferrets are thought to have declined in number as a result of the poisoning of prairie dogs, their prey.
选项 A、black-footed ferrets are thought to have declined in number
B、it is thought that the decline in number of black-footed ferrets is
C、the decline in the number of black-footed ferrets is thought of as
D、that black-footed ferrets have declined in their numbers is thought to be
E、the numbers of the black-footed ferrets are thought to have declined as
答案 A
解析 句首是once引导的时间状语的省略形式，由此省略形式决定了B、C、D、E(it，the decline和the numbers)均不能作主句的主语，而主句仅能由black—footed ferrets担任。只有A项符合此要求，其中用了动词不定式的完成体，表明decline是发生在think之前的动作。
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