同学们， as与 which大家都非常熟悉,它们都能引导非限定性定语从句，但是它们在引导非限定性定语从句时有哪些区别呢？赶快来看一下吧！

由 as， which引导的非限定性定语从句。 as和 which可代整个主句，相当于 and this或 and that。 As一般放在句首， which在句中。

As we know, smoking is harmful to one's health.

The sun heats the earth, which is very important to us.

as可引导非限制性从句，常带有“正如”的意思。

As is know, smoking is harmful to one's health.

As we all know, he never smokes.

用法区别：

( 1) as引导的定语从句可置于句首，而 which不可。

We should have such a dictionary as he is using.

( 2) as代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用 which。

She succeeded in her doing the research work, as we expected.

( 4) As的用法 the same… as； such… as中的 as是一种固定结构，和……一样……。

I should like to use the same tool as is used here.

( 3)非限定性定语从句中出现 expect， think， suppose等表示猜测、想象、预料等时。

同学们，对于 as与 which不再是傻傻分不清楚了吧，一定要学会正确的使用它们，在考试中避免犯错误！