Since nobody gave him any help, he have done the research on his own. A. can B.

 Since nobody gave him any help, he ______ have done the research on his own.

A. can                      B. must                 C. would               D. need

试题答案

 B。本题考查情态动词虚拟语气。由“没有人帮过”可以推断出“一定是他自己做的”，而must have done的意思就是“一定做过某事”，表示对过去发生的事情的推测。

【拓展】情态动词可以表示对过去发生的事情的推测：may/might have done可能做过；must have done 肯定做过；can’t/couldn’t have done 不可能做过；should have done 本该做但没做；shouldn’t have done 本不该做但做了；need have done本来有必要做但没做； need’t have done 本没必要做但做了。

【句意】既然没有人帮助过他，那他一定是自己做的这项研究工作。