He have finished his work; otherwise, he wouldn’t be enjoying himself by the seaside.
A. should
B. must
C. need
D. can
网友回答
A. should
(答案→)B. must
C. need
D. can
解析：考查情态动词表推测的用法。句意“他一定已经完成作业了，不然，他他不可能正在海边玩。”should have done“本应该做某事”；must have done“一定已经做了某事”；can have done“可能已经做了某事”。本题表肯定的推测。故选B。