when引导的句子前后可以都是过去式吗?

问题描述:

when引导的句子前后可以都是过去式吗?
我们老师好像说前后不能都是过去进行时,前后失态要不一样.

可以.举个例子:When the teacher came in to the classroom,she found all the students were asleep.