I didn't know what--------then.A.he was doing B.was he doing C.he is doing D.is he doing

问题描述:

I didn't know what--------then.A.he was doing B.was he doing C.he is doing D.is he doing

A.he was doing 宾语从句,时态和主句保持一致,C时态不对;因为是从句,要用陈述句,B和D是特殊疑问句.