补充250中207

语法知识点核对：

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 enteredfficeffice" />

(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

1、白令海峡一直被以为是……，所以用一般时态；

2、而后面的to have entered 是过去完成时的不定式样子；

3、first 是起先的意思，at first 最开始

right?