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as引导限定性定语从句
定语从句（也称关系从句、形容词性从句），是指一类由关系词引导的从句，因为这类从句的句法功能多是做定语，所以曾被称为定语从句，这类从句除了可以做定语之外，还可以充当状语等其他成分，所以现代语言学多使用“关系从句”这一术语。以下是小编帮大家整理的as引导限定性定语从句，欢迎大家借鉴与参考，希望对大家有所帮助。
as引导限定性定语从句
as作为引导定语从句的关系代词，它既可以用于限制性定语从句，又可用于非限制性定语从句之中。但是，as引导限制性定语从句和非限制性定语从句时有着根本的不同。
as用于限制性定语从句：
as引导限制性定语从句只能用在一些固定结构中，即只能用在such， the same as修饰的先行项的后面。例：He is not such a man as would leave his work half done.此时such与as构成结构上的呼应关系，假如句中没有such这个词，此时就不能使用as，那么此句就要改为：He is not a man who would leave his work half done. 此外，as在引导非限制性定语从句时，其先行词可以是人，也可以是物，所以只需根据先行项中有无such和the same来判断是否使用as就可以了。
1、as引导限制性定语从句的主要结构有：the same…as；as…as；such…as；so…as。主句中出现the same, as, such, so修饰先行词，需选择as做关系代词在定语从句中做主语或宾语。例，It’s the same person as we wanted to find yesterday .
2、as引导非限制性定语从句，指代整个主句内容，从句可置于句首，句中或句尾。
例：As everyone knows ,China is a beautiful country with a long history .
3、非限制性定语从句中的谓语为被动式时，常用as做主语。例：be said/known/announced/reported/mentioned/expected/discussed
as用于非限制性定语从句：
as引导的非限制性定语从句特点有二：一是先行项通常为一个句子，二是as在句中位置较为灵活，可以在句首、句中、句尾。此点有别于which引导的非限制性定语从句。我们知道，which在引导非限制性定语从句时，其先行项通常也为一个句子，但是which引导的非限制性定语从句是不可以放在句首的，这是二者的重要区别。例：
The earth is round，which/as is known to all.
As is known to all，the earth is round.
在第一个句子中，非限制性定语从句的位置在句尾，此时which和as两者都可使用，而在第二句话中，显然此时非限制性定语从句的位置挪到了句首，那么此时就只能选用as这个词了。
定语从句中不太常见但又很重要的关系代词，除了as之外，还有than，but，what等等。
非限定性定语从句as引导
as引出非限定性定语从句时，代替整个主句，对其进行说明但通常用于像as we all know, as it is known, as is known to all, as it is, as is said above, as always mentioned above, as is usual, as is often the case, as is reported in the newspaper等句式中。as在非限定性定语从句中作主语、表语或宾语，且引出的从句位置比较灵活，可位于句首或句末，也可置于主句中间。通常均由逗号将其与主句隔开。as有“正如……， 就像……”之意。
如：As is known to the United States, Mark Twain is a great American writer.
美国人都知道，马克·吐温是一位伟大的美国作家。（as在从句中作主语）
He forgot to bring his pen with him, as was often the case.
他忘了带笔，这是常事。（as在从句中作主语）
He is absorbed in work, as he often was.
他正在全神贯注地工作，他过去经常这样。（as在从句中作表语）
As we all know, the earth is round.
众所周知，地球是圆的。（as在从句中作宾语）
The two brothers were satisfied with this decision，as was agreed beforehand.
两兄弟对此决定都满意，这项决定在事前都已得到他们的同意。(as在从句中作主语)
Taiwan is，as you know，an inseparable part of China.
你知道，台湾是中国不可分割的一部分。(as在从句中作宾语)
“介词+关系代词”引导非限制性定语从句：在介词后引导非限制性定语从句。
难：句意相同
as it is known to all (that...) (as 做状语从句连词，是状语从句, 可以加that)
与 as is known to all (as做主语，是定语从句)
与 it is known to all that... (主语从句，it是形式主语)
即：As is widely known, the moon is closer to the us than the sun.(定从)
= That the moon is closer to the us than the sun is widely known.(主从)
= It is widely known that the moon is closer to the us than the sun.(主从)
As it is known to everyone, I thought you knew about it too.(状从)[1]
关系代词which有时并不代表主句中某一确定的词，而是概括整个主句的意思。介词的选择取决于它与先行词的搭配或与从句中谓语动词的搭配。
They were short of sticks to make frames for the climbing vines，without which the yield would be halved.
他们缺搭葡萄架的杆儿，没有它们产量会减少一半。
They thanked Tom，without whose support they would not have succeeded.
他们很感激Tom，没有他的支持他们是不会成功的。
As 的用法
例1. the same… as；such…as 中的as 是一种固定结构, 和……一样……。
I have got into the same trouble as he (has).
例2. as可引导非限制性从句，常带有正如。
As we know, smoking is harmful to ones health.
As is know, smoking is harmful to ones health.
As是关系代词。例1中的as作know的宾语；例2中，它充当从句的主语，谓语动词know要用被动式。
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