在非限制定语从句中用which，as有什么区别

在非限制定语从句中用which，as有什么区别

解答: 
which 和as 都可以引导非限制性定语从句，它们的先行词都可以是前面的整个句子，但在用法上有区别。它们的区别是：
which引导的非限制性定语从句必须置于主句之后，而as引导的非限制性定语从句可以置于句首、句中和句尾。例如：
1)She has been admitted to Beijing University, which / as is true.她考上北京大学了，这件事是真的。
2) As is known to all, China is famous for the Great Wall. 众所周知，中国以长城而闻名。
3)Taiwan, as is known to all, belongs to China. 众所周知，台湾是中国的一部分。
4) China is a developing country, as is known to all. 众所周知，中国是一个发展中国家。

   2. as有“正如……，正像……”的意思，而which则没有。例如：
1）As you can see, we're still working. 如你所见，我们仍在工作。
2）There are two people who have been admitted to Shandong University , as we expected. 正如我们所预料的，有两个人考上山东大学。
   3. which可以用在名词之前，而as则不可以。例如：
1）He has been absent from work for two months, in which case the boss will have to consider dismissing him. 他已经旷工两个月了，既然这样，老板将不得不考虑解雇他。

2）Mary is in hospital, for which reason she cannot go to school. 玛丽住院了，由于这个原因，她不能去上学。

在非限制定语从句中用which，as区别:
1.as引导非限制性定语从句，只代表主语或主句的一部分所表达的意思(不能指代某个名词或代词)，可以放在主句前，后或中间，在从句中作主语或宾语、例如：
As is known to all, he is the best student in our class. (as指代整个句子，作主语，置于句首)
He opposed the idea, as could be expected. (as 指代整个句子，作主语，置于句末)
As we all know, he studies very hard. (as 指代整个句子，作宾语，置于句首)
Taiwanis, as you know, an inseparable part of China. (as指代整个句子，作宾语，置于句中)
2.在非限制性定语从句中，which和as引导定语从句时的区别：
a. which引导的从句不能放在主句前，而as引导的从句则既可以放在主句前，也可以放在主句后。
b.用能做关系代词，as和which都可以指代一个句子，但as有“正如”、“就像”之意，which则没有此含义。
He is a foreigner, as I know from his accent. (as指代一个句子，意为“正如”、“就像”)
He has to work on Sunday, which he doesn’t like. (which指代一个句子，没有“正如”、“就像”)
c.当从句的谓语动词是be或相当于联系动词的seem, become等时，可用as或which作主语。但当从句的谓语是行为动词时，只能用which作主语。

区别：
1、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 to all, 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 she won the match, which was a lie.
The material is elastic, 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as做主语时，谓语常用系动词，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 say anything at the meeting , as/which seemed very strange.
4、as常用“正如”含义，常用的结构有as we know（众所周知）；as often 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 for school, as often happened.
5、 在非限制性定语从句中which指代主句中某一个单词时，as不可以。
My brother enjoyed playing basketball, which he really plays well.
Beijing, which he was born in, is our capital.
6、“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 mixture of gases, of which oxygen forms 21 percent.
7、从句中的谓语动词是否定形式时，常用which。
He can write a letter in English, which I can not.
Metal will bear beating with a hammer, which a stone will not
8、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 had passed the exam, which was untrue.