They when the teacher came in.A. talk B. are talkingC. to talkD. were talking

问题补充：

They when the teacher came in.

A. talk

B. are talking

C. to talk

D. were talking

答案：

A. talk

B. are talking

C. to talk

(答案→)D. were talking

解析：句意：当老师进来时，他们正在说话。结合语境可知主句描述的是过去某时正在进行的动作，故用过去进行时态。选D。