when和while引导,意思上都差不多.关键是时态搭配. when引导的时间状语从句,一般是两个情况,一个是主将从现,比如I will visit you when I am free.还有一个是从句用一般过去时,主句用过去进行时,比如I was reading a book when he came. while引导的时间状语从句,你只要保证从句用进行时就可以了,主句无所谓,当然一般主句也用进行时,比如I was reading a book while he was watching TV.
