英语什么情况用as 做引导词如题
当先行词为前面的整个句子时，非限制性定语从句的关系代词用as。as引导的非限制性定语从句可以置句首、句中、句尾。如:
China is famous for the Great Wall, as is well known.
As we all know , China is famous for the Great Wall.
China, as we all know , is famous for the Great Wall.
当先行词为same、such或者先行词被这两个词修饰时，后面的定语从句用as.如：
This knife is the same (knife) as I saw that day.
I've never heard such (stories) as he tells.
引导状语从句的连词as可以用作关系代词，引导定语从句，因而被称作准关系代词。
1. 准关系代词as引导限制定语从句，用于以下3个结构中，as在从句中作主语、宾语或表语：
a. so / such…as
Such people as were mentioned by him were honest. (as作主语)
I’ve never seen such a clever man as he is. (as作表语)
Last term our maths teacher set so difficult an (= such a difficult) examination problem as none of us worked out.
b. the same…as
Modern statemen are often faced with the same problem as defeated the ancient Romans. (as 作宾语)
I like the same book as you do. (as 作宾语)
c. as…as
As many children as came were given some cakes. (as 作主语)
He is as diligent a man as ever lived. (as 作主语)
补充：
a. such…as 与 such…that的区别
such…as 引导定语从句；such…that引导结果状语从句。
They talked in such simple English as children could understand.
他们用孩子们能听懂的简单的英语交谈。
They talked in such simple English that children could understand it.
他们用十分简单的英语交谈，连孩子们都能听懂。
I will provide you with such things as you may need.
我要供给你一些你可以用得着的东西。
He shut the window with such a force that the glass broke.
他如此用力地关门，结果玻璃碎了。
b. the same…as与the same…that的区别：
the same…as指两物相似，the same..描述的是同一物。
This is the same bag as I lost yesterday.
这个书包和我昨天丢失的（书包）相似。（相似物）
This is the same bag that I lost yesterday.
这正是我昨天丢失的那个书包。（同一物）
2. 准关系代词as引导非限制定语从句。
a. 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)
Taiwan is, as you know, an inseparable part of China. (as指代整个句子，作宾语，置于句中)
常用的这类句式有：
as is said above 综上所述 - as is known to all 众所周知
as is often the case 通常如此 - as is reported in the newspaper 如报纸所报导的
b. 主句具有否定意义，as引导的定语从句位于主句之后时，as指代得主句不包括否定意义，并可用but取代。例如：
Whales are now fish, as some people think / but some people think they are.
I am no orator, as Brutus is.我不善言词,而勃鲁特斯却是个雄辩家.
Spiders are notinsects,as many people think, nor even near1y related to them.
蜘蛛不是昆虫,尽管许多人认为它是昆虫,它甚至与昆虫几乎没有关系.
但as引导的定语从句谓语主句前时，as指代的主句仍包括否定意义。
As has been said above, grammar is not a set of dead rules.
正如前面所说的，语法不是一套死条纹。
3. 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。
4. as 可用作连词，引导状语从句，构成省略形式“as + 过去分词”这一特殊结构，译成汉语时作用如定语。例如：
The bridge as shown in the picture is really wonderful. (as shown = as it is shown 可译为“图中的桥”)
See the answers as given at the end of this book. (as given = as it is shown 可译为“书后给出的答案”)
English as spoken is Australia is slightly different from British English.
(as spoken = as it is spoken 可译为“在澳大利亚讲得英语”)
请看下列的“as + 过去分词”结构用于修饰前面的名词：
The study as described in the article… 如文章中描述的那种学习
The program as conducted by… 由…指挥的（指导的）节目
The art as applied to medicine… 应用于医学的艺术
The products as seen on TV…电视上看到得产品
希望可以帮到你，as既可以用作连词,引导多种状语从句，也可以用作关系代词引导定语从句.
引导时间状语从句,
作"当……的时候",其特点为：
表示同一个人的两种动作交替进行,"一边……,一边……"
The girl dances as she sings on the stage. 这个孩子在舞台上载歌载物.
He looked behind from time to time as he went forward. 他边走边不时地回头看.表示两个同步发展的动作,"随着……"
As time went on / by, she became more and more worried. 随着时间的流失,她越发担心.
As children get older, they become more and more interested in the things around them. 随着年龄的增长,他们对周围的事物越感兴趣.表示两个短促行为或事件几乎同时发生.:
I thought of it just as you opened your mouth.
后接名词表某一年龄段时,用as.如:
As a young man（=When he was a young man）, he was active in sports. 年轻时,他在运动上很活跃.引导方式状语从句
作"像"、"按照……的方式"
You must do everything as I do.你必须要照我的样子去做.在as...as...或not so/ as...as...中,前一个as是副词,后一个as是连词,它所引导的比较状语从句多使用省略形式.如:
They helped the old man as often as (it is) possible. 他们尽可能经常地帮助那位老人.
关于as...as的常见句型
1as...as possible （等于as … as sb. can/ could）
Please answer my question as soon as possible.请尽快回答我的问题.
2 as...as usual/before
She looks as pretty as before.她看起来和以前一样漂亮.
as busy as a bee像蜜蜂一样忙碌
as easy as ABC 像ABC一样容易
as deep as a well 像井一样深
as light as a feather像羽毛一样轻
as soft as butter 像黄油一样软
as rich as a Jew 像犹太人一样富裕
5. 引导让步状语从句
倒装1）提前表语（单数可数名词做表语时要省略冠词）2）提前状语3）提前动词原形.例如：
Child as he was, he knew what was the right thing to do. 尽管他是个孩子,他却知道什么是该做的事情.
Try as he might, he failed in the exam. 尽管他努力了,可还是考试没及格.
Much as I like it, I can’t afford the laptop. 虽然我非常喜欢这部笔记本电脑,我却买不起.
注意与though和although的区别：although 和though也可以引导让步状语从句,含义是“虽然,尽管”,但as所表示的语气较强,引导的让步状语从句用倒装语序；although语气稍正式些,它所引导的从句可放在句首,也可放在句中,主句中不能再用but,但可以用yet,它所引导的从句不能倒装；though引导的让步状语从句最为常用,它所引导的从句既可和as从句一样倒装,也可以使用正常语序.另外though和although所引导的从句在主句的主语和从句的主语一致,且从句的谓语动词有be时,从句的主语和be动词可以省略.例如：
Although he is quite old, he still jogs every day.他虽然年纪相当大,仍然每天慢跑.
Though (it is) not very large, the room is very lit and comfortable to live in. 尽管房间不大,但采光很好,而且住起来很舒服.
Although (he was) born in Chicago, the author is most famous for his stories about New York City. 这位作家虽然出生在芝加哥,但他却以关于纽约的故事而闻名.
6．用作关系代词引导定语从句.
关系代词as引导定语从句时,既可以引导非限制性定语从句,也可以引导限制性定语从句.as引导限制性定语从句时先行词一般被the same, such等词修饰时.例如:
Such a good film as you described is well worth seeing.你所描述的这么一部好电影是很值得一看的.
I’m reading the same book as he bought yesterday. 我在读一本和他昨天买的一样的书.
as引导非限制性定语从句时,先行词通常是一个句子或句子中的一部分.例如：
She is late, as is often the case.她迟到了,这是经常的事.(先行词是整个主句)
To shut your eyes to facts, as many of you do, is very foolish.对事实视而不见--你们好多人都是如此,是非常愚蠢的.(先行词是不定式短语)
注意和which引导的非限制性定语从句修饰一个句子时的差异：1）as引导的定语从句的位置十分灵活,可以置于主句的前或后,也可以插在主句的中间,而which引导的定语从句只能置于主句的后面.例如：
As we all know now, heavy objects and light objects fall at the same speed unless air holds them back.
= Heavy objects and light objects fall at the same speed unless air holds them back, as we all know now.
= Heavy objects and light objects, as we all know now, fall at the same speed unless air holds them back. 正如我们都知道的那样,轻重物体以相同的速度下降,除非是空气阻碍它们.
Bamboo is hollow, which makes them very light.竹子是中空的,这使竹子非常轻.
2）as在指代所修饰的句子,依然保留着其作为连词的含义,正如,好像,像……；which仅单纯地指代其所修饰的句子所体现的含义.
As we expected, he succeeded in passing the exam. 正如我们所预料的那样,他通过了考试.
He was late this morning, which surprised us very much. 今天早上他迟到了,这让我们非常惊讶.
3）as 多在从句中作宾语,仅在as is known、as is reported、 as is said、 as is announced等被动形式的定语从句中作主语；which多在从句中作主语,但当非限制性定语从句中有宾语补足语时,which也可以作宾语.
Great wrong was done to him, as anyone can see. 他蒙受了巨大的冤屈,这是尽人皆知的事情.
Lisy told a lie, which her parents found strange. 莉莉撒谎了,她父母对此感到很奇怪.
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