—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
网友回答
A. did
B. has done
(答案→)C. was doing
D. had done
解析：考查时态题。题意为“他今天上午在做作业，但是我不知道他现在是否做完了”，用过去进行时强调过去某时正在做某事，另外，过去进行时，还表示动作的未完成性。故最佳答案为C。