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。