which与as引导非限制性定语从句的异同
which与as一样，都可以引导非限制性定语从句，它们既有相同之处，也有差别。因此在实际运用中容易混淆。它们的某些用法在高考中也会考查。
一．相同点。
两者引导非限制性定语从句时，可指代主句中的部分或整个句子的内容，在从句中做主语，宾语或表语，位于主句之后有时可互换。
The meeting was put off, as /which was exactly what we wanted.
He was a doctor,as/which I knew from his manner.
不同点
1. as可指其前后主句提到的事实或情况，因此引导的非限制性从句位置比较灵活，as可以放在主句前后，也可插入主句之中；而which引导的非限制性从句只能位于主句之后。
As is known toall, fish can’t live without water.
Air, as we know,is gas.
2.在非限制性从句中，which后的be动词不可省；as而后的be动词可以省略。
She told me shewon the match , which was a lie.
The material iselastic, as (was) shown in the figure.
3. which在非限制性定语从句做主语时可用各类动词做谓语；而在非限制性定语从句做主语时，谓语常用连系动词，如be, seem, become等，一般不用其他行为动词。
He saw the girl,which delighted him.
He didn’t sayanything at the meeting , as/which seemed very strange.
4. 如果主句中叙述的事情与从句所涉及的意向一致，多用as，用以对主句的意义进行补充；如果不一致，就用which
She has married again, as was expected.
He broke the rules again, which was unexpected.
5.如表示“如同。。。那样，按照，正如”含义，常用as，这里as主要起与上下文联系的作用，表达说话人的看法，并指出内容，出处和根据等，常用的结构有as we know（众所周知）asoften happens（正如常发生的那样）as is often the case（情况常常如此）as we all can see（正如我们看到的）be+announced/expected/known/imagined/mentioned/said/shown/reported（正如所。。。）等。这些结构常放句首，偶尔也可以放句中或句末
As is known to all, China is a developing country.
Kate was late forschool , as often happened.
6.在非限制性定语从句中关系代词指代主句中某一个单词时，常用which
My brother enjoyedplaying basketball , which he really plays well.
Beijing , which he was born in, is our capital.
7.在非限制性定语从句中“介词+关系代词（介宾代物）”中关系代词只能用which
The Travel Agency, with which our company has been dealing for several years, has opened for new branches
Air is a mixtureof gases, of which oxgen forms 21 percent.
8.有时用case, point, time, situation或reason等抽象名词来总结主句的内容，可用“介词+ which +抽象名词”构成从句
Ten years of hard work changed her greatly , for which reason he could hardly recognise her at first sight.
The machine may beout of order , in which case it will be repaired at once.
9.在非限制性定语从句关系代词用以代表主句中谓语的整个概念，从句中的谓语动词是否定形式时，常用which
He can write aletter in English, which I can not.
Metal will bearbeating with a hammer, which a stone willl not
10.在非限制性定语从句关系代词代表前面主句中的宾语从句时，常用which
He said he hadpassed the exam , which was untrue.
这些都是教程内容。
追问请问什么教程？
追答非限定性定语从句
as 与 which 区别
其实我建议你最好翻阅一下语法书。
很多四级教程的语法题上都会讲到。
根据书上所说的，自己综合理解，再加上网上的，你会理解得更好。
因为语法的东西最主要在于理解。