He have completed his work; otherwise he wouldn’t be enjoying himself by the seasideA.

问题补充：

He have completed his work; otherwise, he wouldn’t be enjoying himself by the seaside．

A. should

B. must

C. wouldn’t

D. can’t

答案：

A. should

(答案→)B. must

C. wouldn’t

D. can’t

解析：must have done表示对于过去动作所做的确定的推断，意为“（过去）一定做了某事”。根据He wouldn’t be enjoying …推断，他一定完成了工作。should have done表示“（过去）该做某事而没有做”；wouldn’t have done表示“（过去）实际上做了某事”； can’t have done表示对于过去动作否定的推断，意为“（过去）不可能做了某事”。故答案为A.