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as 引导从句的用法
（一） as作为从属连词，可以引导下列从句：
1． 时间状语从句，意为“正当。。。的时候”、“一面。。。一面”、“随着”，从句可放之前或之后。
1),As I was coming here， I met your brother。
2),As he walked on，he felt himself getting more and more tired。
2, 原因从句，“由于”大多位于主句之前，偶尔在前或后。
3),As this question is of great importance， we will discuss it once again。
4),Water，as it occurs in natrue， is never very pure.
5),We couldn‘t send the children to school as life was very hard in those days 。
3, 方式状语从句， “如同”、“按照。。。。的方式、样子、办法”。As从句总跟在主句之后。
6). You must try to hold the tool as I do 。象我那样拿住工具。
7),Leave things as they are。让那些东西保持原样。
3, 让步主语从句，“虽然”，多在主句之前，且多用倒装。（应将从句主要成分的形容词、副词、原形动词、不加冠词的单数名词置于as 前面）
8). Difficult as it is，we should not give it up。
9),Child as he is ， he knows something about electricity。
4, As引导比较状语从句，“和。。。。一样/不一样”。As。。。as。。。，not as/so。。。as。。。
前一个as、so 是副词“那么”“如此”后一个为连词，引导的比较状语从句常常用省略。
10), The line AB is as long as the line CD （is）。
11), I haven‘t seen as/so interesting a film as this for years。
可以在“as。。。as。。”结构前加上表示程度或倍数的词语，如：just ， nearly ， almost，twice， three times或“倍数+ as many/ much。。。as。。。”结构。
12), This is just as important an experiment as that （is）
13), There are now three times as many schools in this city as （there were ）ten years ago 。
（二） 作为关系代词，可以引导定语从句，在定语从句中充当主语、宾语、介词宾语、表语，可以指人也可指物
         1。引导限制性定从。The same。。。as。。。/ such。。。as。。。/ as （many、 much、   few、 little。。。。）as
 14), He isn’t the same person as he used to be.
 15), I have never heard such story as he is telling.
 16) As many instruments as are in the laboratory have been made most use of.
  实验室里有那么多的仪器被用上了
2． 引导非限制性定从，修饰整个主句或主句的一部分，可在句首、句中、句末。当 as 在从句中做主语时，从句的谓语动词常是被动语态或系表结构。在从句中做宾语时，从句的谓语动词常是情态动词 + 动词原形。
17).  As is often the case, we have overfulfilled the production plan.
18), This machine, as might be expected, has stopped operating.
19), He came very early this morning, as (was) usual.
此外还有:
As has been said before/   as may be imagined  / as is well known/  as we all can see/  as often happens/  as has already been pointed out
       练习:
     1, ____the day went on. The weather got worse.
            A/ with    B, since   C, while    D,as
2/ Mother was worried because little Alice was ill, especially____ Father was away in France.
       A,  as       B, that      C, during    D, if
     3, we’d better hurry _____ it is getting dark.
    A, and    B, but  C,  as   D, unless
4,____ , he doesn’t study well.
   A, As he is clever    B, he is as clever  C, clever as he is  D, as clever he is
5,_____,I have never seen anyone who’s as capable as John.
  A,As long as I have travelled     B, now that I have travelled so much
  C, Much as I have travelled      D, as have travelled so much
6, ____ is mentioned above, the number of the students in senior high schools is increasing.B, as   C, that  D,  it
7. ____ is known to all . China will be an ____ and powerful country in 20 or 30 years’ time .
 A, That , advancing   B,This, advanced   C, As , advanced  D, It, advancing
8, ____ is known to everybody, the moon travels round the earth once every month.
  A, It       B, as     C, that      D, what
9/ John plays football ____ , if not better than, David.
   A, as well   B, as well as   C,so well  D, so well  as
10/ she doesn’t speak ____ her friend, but her written work is excellent.
  A ,as will as  B, so often as    C, so much as  D, as good as
11/ the horse is getting old and cannot run _____it did.
   A, as faster as   B, so fast than   C, so faster as  D, as fast as
12/ after the new technique was introduced, the factory produced ____ tractors in 1988 as the year before.
  A, as twice many  B, as many twice  C, twice as many D,  twice many as
13/ with the help of the German experts, the factory produced _____ cars in 1993 as the years before.
  A, as twice many  B, as many as twice  C, as twice as many D, twice as many
14/ Americans eat ____vegetables per person today as they did in 1923
  A, more than twice  B, as twice as many   C, twice as many as  D,  more than twice as many
15/ These houses are sold at such a low price _____ people expected.
   A,  like   B,  as  C,  that     D, which
16/ It is generally believed that teaching is ______ it is a science.
   A, an art much as  B,much an art as C, as an art much as  D, as much an art as
17. I am at least ____ age ____ Robert if I am not older than he .
   A, the same , as     B, the same, with   C, as same, as   D, as same , with
18/ The piano in the other shop will be _____ but _____.
    A. cheaper, not as better       B. more cheap , not as better
C, cheaper, not as good         D, more cheap , not as good
      1---5 DACCC    6---10 BCBBA  11---15 DCDDB    16--18DAC
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