关系代词which和as如何区分

(1)位置上，as可放在句首、句末，也可插入主句中;which一般放在主句之后(有时也可用as)：

As we all know, reading is very important.

Reading is very important, which we have already known when we were very young.

(2)意义上，as有正如、按照、正像之意，一般用在肯定句中;which可用于含肯、否定意义的句子中：

He failed in the exam again, as was expected.

He failed in the exam again, which was unexpected.

(3)当定语从句所修饰的主句内容是谓语动词的对象时，常用as，如：

Jack was admitted into the university, as we had expected.

(4)固定结构，用as：

as has been said before as often happens

as is well known as we all can see

the same...as such...as

(5)当关系代词代表主句引起的结果，又做主谓宾补(SVOC)结构中的主语时，多用which：

He passed the exam, which made him delighted.

(6)在从句中作介词宾语时，用which，如：

They went to the zoo, after which they saw a film.

(7)在从句中代表主句中的谓语的整个概念时，常用which，如：

He can write a letter in English, which I cannot.

(8)指代主句中某一名词时，多用which，如：

Beijing, which he was born, is our capital.

(9)代替主句中的形容词时, 常用which，如：

Lily thought me clever, which she herself was.