Question

When they saw their teacher         into the classroom, they stopped         at once.

A. walk; to talk                                B. walking; to talk

C. to walk; talking                             D. walking; talking

Answer

D

【解析】

试题分析：句意：当他们看到老师进入教室，他们离开停止了交谈。see sb doing sth看到某人正在做某事；see sb do sth,看到某人做了某事。stop doing sth,停止正在做的事情，stop to do sth,停下来去做某事。根据句意可知学生看到了老师进来，停止了正在做的动作，结合结构，故选D。

考点：考查非谓语动词的用法。