-Has Sam finished his homework today?-- I have no idea. He it this morning.A. didB

问题补充：

---- 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

答案：

A. did

B. has done

(答案→)C. was doing

D. had done

解析：考查时态。句意：今天Sam完成作业了吗？我不知道，他今天上午在做。表示过去某一时刻进行的动作用过去进行时态。根据题意上午那个时刻他在做作业，故选C。