— Has Jack finished his homework yet?
— I have no idea；he ＿＿it this morning.
A. was doing
B. had been doing
C. has done
D. did
网友回答
(答案→)A. was doing
B. had been doing
C. has done
D. did
解析：题干没有构成“过去的过去”，不可选B。如选C、D则表示动作已完成，与have no idea相矛盾。过去进行时表示过去某段时间或某一时刻正在进行的动作，不涉及结果，正好附合题干语境。