as,which都可以引導(dǎo)非限制性定語從句,但倆者適用的場合不同,是不能互換通用的.
1.如果非限制性定語從句的先行詞是一件物,不是整個句子,那只能用which,不能用as.
My house,which I bought 1n 2008,is worth 1500 thousand yuan by now ,just ten times as much as that 14 yers ago.
2.如果非限制性定語從句的先行詞是整個句子,除了下面3所指的特殊情況外,都只能用which,不能用as：It has rained a lot ,which makes the level of the river rise .
3.如果非限制性定語從句的先行詞是整個句子,從句動詞又與人的經(jīng)驗知識認(rèn)知有關(guān),又有~正如.一樣~的意思時,正如大家那知道的一樣~正如大家都能看得出來,正如你懂的~正如我們所預(yù)料的一樣,那就只能用as不能用which.例：As we know,the earth is round .As everybody can see,Dawei loves Sussan deep in his heart ,but he dare not to say it out .
4.在限制性定語從句中,如果先行詞被such,so修飾,只能用as當(dāng)關(guān)系代詞.such.as..."so.as."固定搭配：
He is such a handsome boy that many girls love him .
I am so careless a boy that you mustn`t love .