as 的用法1、as引导的定语从句可放在句首、句中和句尾,which引导的定语从句只能放在句尾.As we all know,the earth is round.David,as you know,is a photograopher.戴维是个摄影师,你是知道的.(不可用which) Li Min

as 的用法1、as引导的定语从句可放在句首、句中和句尾,which引导的定语从句只能放在句尾.As we all know,the earth is round.David,as you know,is a photograopher.戴维是个摄影师,你是知道的.(不可用which) Li Min
as 的用法
1、as引导的定语从句可放在句首、句中和句尾,which引导的定语从句只能放在句尾.
As we all know,the earth is round.
David,as you know,is a photograopher.戴维是个摄影师,你是知道的.(不可用which)
Li Ming is late,as is often the case.李明迟到了,这事是经常发生的.(不可用which)
2、as有时也可用作关系代词 .as引导非限制性定语从句,若as在从句中作主语,其引导的句子可以放在句首,也可以放在句中.但which引导的非限制性定语从句只能放句中.
例句：As is reported in the newspaper ,some artistic treasures(艺术珍品） will be on show at the exhibition on the weekend.
以上两段在书上看到的,我觉得有点矛盾,请问while 在1中说引导的非限制性定语从句只能放句尾.2说放句中,还有as 能引导限制性定语从句么 求详解

as 的用法1、as引导的定语从句可放在句首、句中和句尾,which引导的定语从句只能放在句尾.As we all know,the earth is round.David,as you know,is a photograopher.戴维是个摄影师,你是知道的.(不可用which) Li Min
as可用作连词,引导比较、时间、原因及方式等四种状语从句,应注意的是,引导的比较状语从句往往有省略；引导的时间状语从句一般用一般现在时而不用一般将来时；引导原因状语从句时与“Because”和“since”引导的从句比较起起来语气最弱.
as作介词,意思时“作为”,“以……身份”.例如：He came to China as a tourist five years ago.
而表示像…一样时,like通常作介词用,而介词后面通常接名词,代名词和动名词.
as in Australia“和在澳大利亚一样”.
as……as
AS +adj(原级)+AS
AS +adv(原级)+AS
as soon as 一……就
as soon as possible 尽可能快地
as early as possible 尽可能早的
as carefully as you can 尽可能认真地
as careful as you can 尽可能认真的
1.as是连词,表示“随着”的意义.lives是life的复数,意义是“生活”.

2.as是连词,表示“因为,由于”的意义.wanting是现在分词,表示主动意义,wanting to buy cars=who want to buy cars.
As的用法小结
as可以作连词、介词及关系代词和副词.现将其用法小结如下:
（一）、 as作连词的用法:
1.作“在-------期间,当----的时候”引导时间状语从句.注意与when、 while的用法区别.
①下列情形时,只用as,而不用when或while.
1)用于表示同一个人的两种动作交替进行,指一边----一边.如:
The girl sings as she goes to school.
He looked behind occasionally as he went forward in the forest.
2)表示两个同步发生的动作或行?意思是随着-----的发展.如:
As time went on / by,she became more and more beautiful .
As children get older,they become more and more interested in everything.
3)表示两个短暂行为或事情几乎同时发生.如:I watched her as she read the book.
I thought of it just as you opened your mouth.
Just as the flying worm hit her face,she gave a loud cry.
4)接在名词后面表示某一个年龄段时.如:
As a young man,he was active in sports.
②when作"当……的时候"解,可以指较短的(一点)时间,也可指一段时间.如:When I was at college,I could speak several foreign languages.When the clock struck twelve,I had slept for 2hours.
③ while常表示一段较长的时间或一个过程,强调主句谓语动词与从句谓语动词同时发生.如:Work while you work.Play while you play.
2.As =Since 作"既然"、"由于"解,引导原因状语从句,常用来表示已为人们所知或显而易见的原因或理由.如:As he’s been ill for ages,I will help him.
As / Since you're not feeling well,you may stay at home.
As he wasn't ready ,we went without him.
3.As =in the way that作"像"、"按照……的方式"解,引导方式状语从句.如:
Do as I told you.
Remember,you must do everything as I do.
4.用于as--- as或not / so/ as ---- as中,前一个as是副词,后一个as是连词,引导比较状语从句.如:They helped the old as much as possible.
I don't speak English so/ as well as she does.
5.表示虽然,尽管 等,引导让步状语从句,常用倒装语序,模式为:
adj./adv./ n.+as +主语+谓语+主句.如:Young as he is,he knows much.
Tired as they were,they walked on.
6.表示也------一样.She is a doctor,as was her husband.
（二）、 as作关系代词,引导定语从句,表示正如,这一点.如:
He is very careful,as we all know.
As is well-known,Taiwan belongs to China.
另外,当先行词被the same,such等词修饰时,常用as来引导定语从句.如:
Such a clever girl as she can learn anything quickly.
I was reading the same book as he bought yesterday.
（三）、as作介词的用法.
1.表示好像.如:He dressed as a policeman.
2.表示作为当作.如：I found a job as a guide.
3.当某人是某身份时.如：As a child ,she was sent to abroad.
4.as引导的介词短语大多用作状语,as译为"作为";少数情况可引起宾语补足语.如:
As a Party member,I'll take the lead in everything.(状语)
She works as a model.(状语)
She has me as one of her best friends.(引起宾语补足语)
（四）、作副词的用法 1 表示与------等同.如：This dress is twice as expensive as that one.2 像,如等.如：As before,he remained unmoved.
总之,通过以上的分析,我们对as的词性和用法有了比较全面的理解和把握,才能在实际的运用中做到心中有数,应付裕如.

as可用作连词，引导比较、时间、原因及方式等四种状语从句，应注意的是，引导的比较状语从句往往有省略；引导的时间状语从句一般用一般现在时而不用一般将来时；引导原因状语从句时与“Because”和“since”引导的从句比较起起来语气最弱。
as作介词，意思时“作为”，“以……身份”。例如：He came to China as a tourist five years ago.
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as可用作连词，引导比较、时间、原因及方式等四种状语从句，应注意的是，引导的比较状语从句往往有省略；引导的时间状语从句一般用一般现在时而不用一般将来时；引导原因状语从句时与“Because”和“since”引导的从句比较起起来语气最弱。
as作介词，意思时“作为”，“以……身份”。例如：He came to China as a tourist five years ago.
而表示像…一样时，like通常作介词用，而介词后面通常接名词，代名词和动名词。
as in Australia“和在澳大利亚一样”。
as……as
AS +adj(原级)+AS
AS +adv(原级)+AS
as soon as 一……就
as soon as possible 尽可能快地
as early as possible 尽可能早的
as carefully as you can 尽可能认真地
as careful as you can 尽可能认真的
1。as是连词，表示“随着”的意义。lives是life的复数，意义是“生活”。

2。as是连词，表示“因为，由于”的意义。wanting是现在分词，表示主动意义，wanting to buy cars=who want to buy cars。
As的用法小结
as可以作连词、介词及关系代词和副词。现将其用法小结如下:
（一）、 as作连词的用法:
1.作“在-------期间，当----的时候”引导时间状语从句.注意与when、 while的用法区别。
①下列情形时,只用as, 而不用when或while。
1)用于表示同一个人的两种动作交替进行,指一边----一边. 如:
The girl sings as she goes to school.
He looked behind occasionally as he went forward in the forest.
2)表示两个同步发生的动作或行?意思是随着-----的发展.如:
As time went on / by, she became more and more beautiful .
As children get older, they become more and more interested in everything.
3)表示两个短暂行为或事情几乎同时发生.如:I watched her as she read the book.
I thought of it just as you opened your mouth.
Just as the flying worm hit her face, she gave a loud cry.
4)接在名词后面表示某一个年龄段时.如:
As a young man, he was active in sports.
②when作"当……的时候"解,可以指较短的(一点)时间,也可指一段时间。如:When I was at college, I could speak several foreign languages. When the clock struck twelve, I had slept for 2hours.
③ while常表示一段较长的时间或一个过程,强调主句谓语动词与从句谓语动词同时发生。如:Work while you work. Play while you play.
2. As =Since 作"既然"、"由于"解,引导原因状语从句,常用来表示已为人们所知或显而易见的原因或理由。如: As he’s been ill for ages, I will help him.
As / Since you're not feeling well, you may stay at home.
As he wasn't ready , we went without him.
3. As =in the way that作"像"、"按照……的方式"解,引导方式状语从句。如:
Do as I told you.
Remember, you must do everything as I do.
4. 用于as--- as或not / so/ as ---- as中,前一个as是副词,后一个as是连词,引导比较状语从句。如:They helped the old as much as possible.
I don't speak English so/ as well as she does.
5. 表示虽然,尽管 等,引导让步状语从句,常用倒装语序,模式为:
adj. /adv. / n.+as +主语+谓语+主句。如: Young as he is, he knows much.
Tired as they were, they walked on.
6. 表示也------一样。 She is a doctor, as was her husband.
（二）、 as作关系代词,引导定语从句,表示正如,这一点.如:
He is very careful, as we all know.
As is well-known, Taiwan belongs to China.
另外,当先行词被the same, such等词修饰时,常用as来引导定语从句。如:
Such a clever girl as she can learn anything quickly.
I was reading the same book as he bought yesterday.
（三）、as作介词的用法.
1.表示好像。如:He dressed as a policeman.
2. 表示作为当作。如：I found a job as a guide.
3. 当某人是某身份时。如：As a child , she was sent to abroad.
4. as引导的介词短语大多用作状语,as译为"作为";少数情况可引起宾语补足语。如:
As a Party member, I'll take the lead in everything. (状语)
She works as a model. (状语)
She has me as one of her best friends.(引起宾语补足语)
（四）、作副词的用法 1 表示与------等同。如：This dress is twice as expensive as that one. 2 像，如等。如：As before, he remained unmoved.
总之，通过以上的分析，我们对as的词性和用法有了比较全面的理解和把握，才能在实际的运用中做到心中有数，应付裕如。

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你这么理解就可以了，不管引导限定性还是非限定性的定语从句，as和which的区别就在于as引导的定语从句可以放句首和句中，which引导的定语从句不能放句首。

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