— Has Jack finished his homework yet?— I have no idea；he ＿＿it this morning.A. was doingB.

问题补充：

— 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

答案：

(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。