问题
选择题
The city is believed over by sandstorms from AD200 to AD400.
A．to cover
B．to be covered
C．to have been covered
D．that was covered
答案
答案：C
题目分析：The city与cover之间是被动关系，故用不定时的被动式；cover这个动作发生在believe之前，故用不定式的被动式的完成时，故选C。
点评：不定式的完成时表示的动作发生在谓语动词表示的动作之前，强调动作的先后顺序。