[求助]250---207

ztlbox

207.Geologists believe that the Bering land bridge, over which human beings are thought to have first entered the Americans, disappeared about 14,000 years ago when massive glaciers melted and caused the sea level to rise several hundred feet worldwide.
(A) are thought to have first entered
(B) were thought first to enter
(C) were thought at first to enter
(D) are thought of as first entering
(E) were thought to first enter
为什么A要用完成时，enter 并不是持续性动作。

为什么是are thought 不是 were thought?

E为什么不对？

谢谢

leeon

注意读出这道题的逻辑意思，第二句我给你补一个先行词，people think that human beings entered ...over...。

用现在时表示是现在被认为怎样；这里的现在完成时用的是已完成用法，表示动作在过去的某一时间已经完成，而过去的这个时间不确定，而不定式通常强调的动作还没有发生。所以这里用了现在完成时。