When the teacher came into the classroom we all stopped.A. to talkB. talkC. talkingD. tal

问题补充：

When the teacher came into the classroom, we all stopped.

A. to talk

B. talk

C. talking

D. talked

答案：

A. to talk

B. talk

(答案→)C. talking

D. talked

解析：句意：当老师走进教室的时候，我们都停止说话。Stop doing sth,停止做某事，停下手头正在做的事情；stop to do sth.停下来去做某事，不定式表示将要去做的事情；故选C。