大全325

chenliqiang

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对，E不对，牛牛请教了

laipiyu

两者就是时态上的区别，本句中entered这个动作是一个过程，并且是已经完成的，用完成时态更合适。

而are thought和were thought倒是都可以，现在认为的和过去认为的，respectively。从句义上看表达这两种意思都是有可能的，属于干扰成分，可以不考虑。主要区别就在于enter这个动作。