― Has Jackson finished his work today? ― I have no idea but he it when I saw him this mo

问题补充：

― Has Jackson finished his work today?

― I have no idea, but he it when I saw him this morning.

A. had done

B. would do

C. was doing

D. would have done

答案：

A. had done

B. would do

(答案→)C. was doing

D. would have done

解析：考察时态.句意:今天杰克逊已经完成了他的工作吗?——我不知道，但是当我今天早晨看见他时他正在做。结合语境可知下文描述的是在过去某个时间正在进行的动作，故用过去进行时态。选C。