求助 时间状语从句的一个问题

求助 时间状语从句的一个问题
as,when ,before,until
引导时间状语从句
或是
做 时间状语
时的用法 及区别?
最好举些例子
我总是掌握不好 请达人赐教 不胜感激啦!

as
强调两个动作的同时进行.
when
用法比较平常,通常和while 相比较
I was cooking when someone knocked at the door.
While I was cooking,someone knocked at the door.
此处when 强调动作的突然性,while 表示动作的进行中
before
在……前
It will be not long before we can see other again.
(不就我们就能再见面了)
Until
直到…… 后面可以加时间短语或者句子,句子中通常不用否定.
You should not get off the bus until the bus stopped completely.(此处等于before)
We waited for him until his work was finished.
(此处强调wait这个动作截至到工作完成)