题目

― 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：C解析：根据题干，语境应为“我不知道，今天早晨他还在做”，A为一般过去时，强调在过去某一时间做某事，不强调结果；B为现在完成时，在过去发生，强调对现在的影响；C为过去进行时，指在过去某一时间正在做某事；D为过去完成时，表达过去的过去。所以C为正确答案。

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