怎么去讲时间状语从句

三句口诀：“主现从任、主过从过、主将从现.”
意思是说：
主句是现在时的话,从句随便你用什么时态.
比如：I‘ll tell her the good news when she comes back.
Don’t laugh at me when I make a mistake.(祈使句)
You should be quiet when you are in the library.(含情态动词)
主句是过去式的话,从句用四种过去时态中的一种（过去一般、过去进行、过去完成、过去将来）
比如：When he entered the room,I stopped eating.
When he entered the room,I was eating.
When he entered the room,I had been eating for five minuted.
When he entered the room,I would have finished eating.这个不太恰当,但你能理解就行.
主句是将来时的话,从句用现在时.
I will be a nurse when I grow up.
 
另外,since 引导时间状语从句时,其主句通常要用现在完成时,有时也用现在完成进行时.如：
She has had another baby since I saw her last.从上次我见到她以来,她又生了一个孩子.
He has grown an inch since I saw him.我上次见到他以后他已长高了一英寸.
注：当主句为“It + be + 一段时间”时,则通常用一般现在时代替现在完成时.如：
It’s more than three years now since I saw her last.我们已有三年多没见面了.
 
一些特定句式的时态：
由no sooner...than,hardly [scarcely]…when引出的时间状语从句,其主句通常用过去完成时,从句通常用一般过去时.如：
Hardly had he arrived when she started complaining.他刚到她就抱怨起来.
No sooner had he gone to sleep than the telephone rang.他刚睡着电话铃就响了.
We had no sooner set out than a thunderstorm broke.我们刚出发就下起一阵雷暴.
No sooner had she agreed to marry him than she started to have terrible doubts.她刚同意嫁给他她就开始产生可怕的疑虑.
When you have finished your homework,I will give you 10 dollars.做完作业,我给你十美元.
When he has come back,I have finished my homework.你到家时,我肯定已经完成作业了.
 
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