— Has Sam finished his homework today?— I have no idea． He ______ it this morning.was doing.\x05A． did \x05B． has done\x05C． was doing \x05D． had done A为什么不对

— Has Sam finished his homework today?— I have no idea． He ______ it this morning.was doing.\x05A． did \x05B． has done\x05C． was doing \x05D． had done A为什么不对
— Has Sam finished his homework today?
— I have no idea． He ______ it this morning.was doing.\x05A． did \x05B． has done\x05C． was doing \x05D． had done A为什么不对

— Has Sam finished his homework today?— I have no idea． He ______ it this morning.was doing.\x05A． did \x05B． has done\x05C． was doing \x05D． had done A为什么不对
过去进行时可以表示过去动作的持续,他今天早上一直在写作业.I have no idea,暗示不知道是否他完成了作业.

A是一般过去时态，C是过去进行时态。根据语境，是回答者说他今天早上正在写。

这个地方我觉得它在于强调：早上我可能是看到他正在做作业，但是不知道做没做完。