连词引导时间状语从句主句从句时态

if 引导真实条件句的,主句用一般将来时态,从句用一般现在时态.
If it doesn't rain tomorrow ,we will go fishing .
when 引导的从句,后面是短暂性动词,就是通常是一般过去时态
eg ：when I heard the news ,I felt very happy .
后面是延续性动词,通常是过去进行时态
eg ：When I was listening to music ,the bell rang .
while ：后面常用过去进行时态
eg ：While he was singing ,somebody knocked at the door.
as soon as ：一...就...主将从现
eg ：As soon as I get there ,I will call you .
before ：通常有时态的递进
Before I got home ,my father had gone .
after 和before 的用法是一样的.
not ...until ：直到...才...常用过去时态
I didn't leave home until my father got back .
since ：自从 注意,since 后面一定是一般过去时态,前面是现在完成时态
She has left his hometown since he finished his study .
becuse ,没有什么时态的要求的.