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。