英语中as和which做非限制性定语从句的区别是什么,可以代替整个句子吗?

在非限制性定语从句中,which和as引导定语从句时的区别
a. which引导的从句不能放在主句前,而as引导的从句则既可以放在主句前,也可以放在主句后.例如：
As (正确) is often the case, he is absent.
Which (错误)
He saw the girl, as (正确) He had hoped.
Which （正确）
b.用能做关系代词,as和which都可以指代一个句子,但as有“正如”、“就像”之意,which则没有此含义.
He is a foreigner, as I know from his accent. (as指代一个句子,意为“正如”、“就像”)
He has to work on Sunday, which he doesn’t like. (which指代一个句子,没有“正如”、“就像”)
c.当从句的谓语动词是be或相当于联系动词的seem, become等时,可用as或which作主语.但当从句的谓语是行为动词时,只能用which作主语.
例如：
He married her, as (正确) was / seemed natural.
Which （正确）
He saw the girl, as (错误) delighted him.
Which （正确）