What you at this time yesterday?A. did doB. have doneC. were doingD. are doing

问题补充：

What you at this time yesterday?

A. did, do

B. have, done

C. were, doing

D. are, doing

答案：

A. did, do

B. have, done

(答案→)C. were, doing

D. are, doing

解析：at this time yesterday,昨天的这个时间，过去进行时的标志。过去进行时的结构：was / were +V-ing .结合句意，昨天这个时候你正在干什么？故选C。