Question

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

A．can

B．must

C．would

D．Need

Answer 1

B

考查情态动词和虚拟语气。can have done sth可能已经做了某事；must have done sth一定已经做了某事；would have done表示与过去的事实相反；need have done sth本来需要做某事。句意“因为没有人给他任何的帮助，他一定是自己完成的那项，研究。”根据，句意可知，表示的是肯定的推测，用must，故选B。
【考点定位】情态动词和虚拟语气。