关于AS和WHCIH用法的区别
谈谈AS 和WHICH 作关系代词时的用法异同
1． AS 作为关系代词引导限制性定语从句时，主要用在以下习惯性搭配中； 此外， 它也可以单独使用。 这时不可以用WHICH 代替。
a. such….as 的结构--------- as 是关系代词， 引导定语从句。Such 既可以作形容词，作先行词的定语， 即构成such +名词+as结构； 也可以作代词，充当as的先行词，而构成such as 结构。 如： he returned ti us later in the day with tobacco, matches, and such provisions as were needed. 那天晚些时候他回到我们这里，带着烟，火柴以及我们必须的给养。 （ as 在从句中作主语） / The instrument is not such as I saw on the exhibition. 这台仪器不是我在展览会上看到的那种。 （ as 在从句中作宾语，such 用作代词，充当as的先行词。）
b. the same…..as 结构 ----------- same 是形容词，修饰先行词；也可以是代词，充当as的先行词。 如： It is said that the moon is made of the same kind of matter as exists on the earth. ( 相同物质构成， as作主语) / It was, of course, just the same with the official as it had been with the minister. 当然， 这位官员所遇到的情况和那位大臣所遇到的完全一样。 （ as 在句中作表语， the same 作代词， 作as的先行词）
比较：
1) This is the same bag that I lost yesterday. ( 这正是我昨天丢失的那个书包)
2) This is the same bag as I lost yesterday. （ 这个书包和我昨天丢失的相似）
比较：
1） He was wearing the same shirt that he’d had on the day before. （ 是他前一天穿过的同一件衬衫）
2） A: Is that a new bicycle?
B: No, it’s the same (one) as ( I had) before.
注意： the same 后使用that 有两个限制
① The same 必须充当名词的定语或是在the same 之后暗含着一个one ( the same one )
② That 引出的从句不能是省略句。 而as没有这种限制。
C． As many……as / as much……as 结构-------- 在这个结构中，第一个as是副词， 修饰many or much; many or much 分别接复数可数名词和不可数名词。 第二个as 是关系代词，引导定语从句。 有时many and much 也可以作代词，充当其后as的先行词。
1) As many people as are present agree to go there for holidays. ( 关系代词as在句中作主语) 所有在场的人都同意去那里度假。
2) Take as much paper as you need, but not more than is necessary. （关系代词as在句中作宾语）按需要取纸， 但不要多拿。
3) You may take as many / much as you want.（ many and much 也可以作代词，充当其后as的先行词）你要多少就拿多少。
D． As…as / so…as
在这个结构中， as / so 都是副词， 其后紧接形容词，形容词后通常再接不定冠词a/ an 的单数名词。 即构成as / so +adj+n+as 结构； 第二个as是关系代词，引导定语从句。
1） It was as pleasant a day as I have ever spent. 那是我度过的最愉快的一天。 （ 关系代词as在句中做宾语）
2） We witnessed so great a parade as nobody ever dreamt in pre-liberation days. 我们亲眼看到过在解放前做梦也想不到的那样大规模的游行。 （ 作宾语）
这种结构可以和such…..as 结构换用，但是要注意不定冠词的位置
Here is so big a stone as no one can lift= Here is such a big stone as no one can lift.
E. as 单独使用，引导限制性定语从句
From every corner of the island little people came to see Man Mountain, as they called Gulliver.
( 小人们从海岛的四面八方来看这位被称为人山的格利佛) as 作宾语
2． Which 作为关系代词引导限定性定语从句的时候， 一般不可以用as 来取代它/
1） A dictionary is a book which gives the meaning of words.
2） The cat, which is black and white, is sitting beside her mistress. (主人)
3． 当as, which 作为关系代词引导非限制性定语从句的时候。用以指代位居前面的主句全部意义的时候，两者可以互换。
1） He said that he was invited, which / as was a lie.
2） The elephant is like a snake, as / which anybody can see.
3） As is known to the world, Mark Twain is a great American write.
4） Which is known to the world ( wrong) , ……
注意下列固定结构中的关系代词as 代表整个主句， 一般不能随意变为which
1) as is often the case 情况常常如此
2) as often happens 正如经常发生的那样
3) as has been said before 如上所述
4) as may be imagined 这是可以想象的出来
5) as might be expected 这是可能预料到的
6) as is well known 众所周知
7) as has been pointed out 正如已经指出的那样
8) as we all can see 正如我们大家都能看到的那样
9) as will be shown in 将如……所示
10) as we know 正如我们知道的那样
as / which 引导非限制性定语从句并位于主句之后或之中时，有如下区别
*当从句表达的情况和先前的情况形成对比的时候， 不适合用which
The girl forgot to bring the English textbook to class, as is often the case.
*非限制性定语从句中谓语动词是expect. Think, want, suppose等时候，关系代词一般用as.
He was against the idea, as we had expected.
The police were looking for him, as he thought.
* 当which 在从句中指代的是主句中的单个先行词而不是整个主句时候， 此时不用as 取代which.
This poem, which almost everybody knows, is written by Lu. ( which=this poem) 这首有口皆碑的诗是鲁迅写的。
The book of yours, which I finished reading last night, was very interesting. ( which=the book) 昨天我读完的那本书很有趣。
* as 间或也可以指代主句中的一个短语，which 则可以用来指代主句中的谓语部分。
To take a one-sided view of things, as the six blind men did, is foolish. ( as=to take a one-sided view of things)
He can write a letter in English, which I can’t. ( which-write a letter in English)
