定语从句分为限制性定语和非限制性定语从句，两者都是英语语法学习中的重点和难点，非限制性定语从句在句中主要起补充说明作用，缺少也不会影响全句的理解，这次小编就为大家来讲解一下由which和as引导的非限制性定语从句的区别，一起学起来吧！
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：
?? She finally stopped crying, as we had expected．
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（4）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．
（5）在从句中作介词宾语时，用which，如：
They went into a room, in which the muder happened.
（6）在从句中代表主句中的谓语的整个概念时，常用which，如：
She can both sing and dance, which I cannot．
好了以上就是为大家带来的which和as引导的非限制性定语从句的区别了，希望大家在学习中能够仔细辨析这些区别，最终达到能轻松分辨不同句式，对各类句型都应用自如的水平。
