Question

— Has Sam finished his homework today ?

— I have no idea. He ______ it this morning.

A. did       B. has done        C. was doing      D. had done

Answer 1

C

解析:

根据后面时间状语this morning可判断为过去时，排除B；进行体表示“示完成性，暂时性，感情色彩”。结合上句，不知道Sam是否做完，所以C 项是最佳答案。