since 与 before 的区别?
问题描述：
since 与 before 的区别?
Mr.Green has lived in China since I came here Mr.Green has lived in China before I came here 第一个正确吗?before是不是也可以用于完成时态?
答
before引导的时间状语从句中常用一般现在时,主句用一般将来时.Since引导的时间状语从句中用一般过去时,主句用现在完成时或一般现在时（主语为 it 时）.It will be five years before we meet again.It is five weeks since we came here.