这道英语题选什么?

问题描述:

这道英语题选什么?
can you tell me________at that time? A what they were doing. B.what they are doing C.what are they doing D.what were they doing.
~\(≧皿≦)/~

选A
at that time 指之前的一个时间,表示过去时态,陈述语句