When the teacher walked into the classroom the students at once.A. stopped to talk B. st

问题补充：

When the teacher walked into the classroom, the students at once.

A. stopped to talk

B. stopped talking

C. stop to talk

D. stop to talking

答案：

A. stopped to talk

(答案→)B. stopped talking

C. stop to talk

D. stop to talking

解析：当老师走进班级，学生们应该立刻停止说话，stop doing sth表示停止做某事，与本题题意相符，故本题选B。