as we all know是什么从句
as作“连接代词”，在从句中作成分。此外，这跟as...as...，not so...as...，the same...as...，such...as...等这些比较结构中的as用法相同，不谋而合，实现统一。就是：as一律引导“比较状语从句”，不再有所谓的“as定语从句”。
as用法：
作从属连词引导状语从句
1.时间状语从句Nathan Hale looked around as a British soldier put the rope round his neck.当一个英国士兵把绳索套在他的脖子上时,内森黑尔望着周围。
as引起的时间状语从句的位置可在主句的前面和后面,从句表示的动作常常与主句表示的动作同时进行。as有时可用while或when替换。
2.原因状语从句
例句：As he did not know much English,he got out his dictionary and looked up the word"Cough"由于英语懂得不多,他找出字典查查cough这个词。
Jennydidn'twant to do that,as her parents were very strict with her.因为父母要求很严,珍妮不想那么做。
as引起的原因状语从句的位置可在主句的前面或后面,as一般可用since because替换,只是语气稍弱。
3.方式状语从句Do it as have done照我做的去做。
4.比较状语从句
例句：He jumped up and ran out of the house as fast as he could.他跳起来,尽快地跑出家。
It is not so(as)warm today as yesterday不如昨天暖和。句中前一个as是副词,后一个是连词引起比较状语从句。
5.让步状语从句
例句：Young as she is,Rose has done a lot of work for her mother.虽然年轻,但露丝替她母亲干很多活。
