一边……一边……
As he was going out, it began to rain.
强调两个动作紧接着发生。
As a boy(When he was a boy), he was hopeless at maths.
as+名词，相当于时间状语从句
before
A.Be a pupil before you become a teacher.
Great changes have taken place in China since 1978.
As soon as I arrive in Shanghai, I’ll write to you.
状语从句在主句之前时一般用逗号与主句分开，如从句在主句之后则不必用标点符号。
Mr. Li has been here since he came back.
WhileIunderstand your point of view,Idon’t share it.
While引导让步状语从句，相当于although，但一般位于主句之前。
While there is life, there is hope.
While引导条件状语从句，相当于as/so long as,翻译成“只要”
as
He hurried home, looking behind as he went.
as引导持续性动作，强调主句和从句的动作同时发生
AsIget older,Iget more optimistic.
两种正在发展或变化的情况，有“随着”的意思，表时间的推移。
He hurried home, looking behind as he went.
B“还没有……”“免得”“不知不觉”“宁可、宁愿”“否则，要不然”
It will be five years before he returns to his homeland.
It won’t be long before we meet again.
状语从句
种类
从属连词
例句
说明
时
间
状
从
when
When I came into the room, he was writing a letter.
We shall go there whenever we are free.
when指的是“某一具体的时间”
whenever指的是“在任何时间”
I was walking along the street when suddenly someone patted me on the shoulder from behind.
It+（not）be+some time+before从句。肯定句中，“多长时间之后才”；否定句中，“用不了多长时间就”
after
He arrived after the game started.
until/till
We waited till (until)he came back .
如主句动词是持续性动作，常用肯定式，表示“直到…为止”
She didn’t stop working until eleven o’clock .
Until he had passed out of sight, she stood there.
如主句动词是瞬间动词，常用否定式，表示“直…才”“在…以前不”,从句放在句首表示强调，一般用until
since
Iwas about to go swimming when our guide stopped me.
when意为“这时”或“在那个时候”,表示某件事正在发生或刚刚发生时，另一动作同时发生。这种用法的when分句一般位于句末。常用句型：be about to do…when…, be doing…when…, had done…when…, be on one’s way…when…, be on the point of doing…when…
Leave me beforeIchanged my mind.
I’d die beforeIapologized to them.
Get out beforeIcall the police.
往往表示主句的动作先于从句的动作发生，“在……之前”，
A.“……才”（强调主句所表达的时间、举例很长或花费的力气很大。）
He usually walks when he might ride.They had only three tables when they needed five.
How can you hope for mercy yourself when you show none?
尽管，虽然，既然，鉴于，如果
Ihave written home but once sinceIcame here.
since后是非延续性动词的过去式，则时间的起点应从该动作发生时算起。
He has written to me frequently since he was ill.
since后是延续性动词的过去式，则时间的起点应从该动作结束时算起。
It is (has been) a long time sinceIsmoked.
It has been two years sinceIbegan to smoke.
while
While it was raining, they went out.
I stayed while he was away.
while指“在某一段时间里”，“在…期间”，while引导的动作必须是持续性的
Ilike watching TV while he likes reading.
while做并列连词，表示相对关系“然而”
BWe waited a long time before he came out
.We hadn’t waited long before he came out.
C．He died before he wrote a will.
D．he sun had set before we knew it.