The students were talking and laughing（ ）the teacher came in.

The students were talking and laughing（ ）the teacher came in.


A、

while


B、

after


C、

since


D、

when


【正确答案】：D
【题目解析】：

如果选since主句要用完成时，不符合。老师进来之后学生不讲话了不用进行时，不选after。while表示两件事情同时发生。选D。句意：老师进来时，学生们在谈笑风生。