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非限制性定語從句which和as的用法
我們知道，as和which作為關系代詞都可以用來引導非限制性定語從句，指代整個主句所表達的內容，在從句中作主語或賓語，但它們在用法上有區別，這一點許多學生往往搞不清楚。以下是小編整理的非限制性定語從句which和as的用法，希望對大家有所幫助。
一、相同之處
當從句位于主句之后，引導詞指代整個主句所表達的全部意義時，as和which可以互換。如：
The elephant is like a snake,as/which everybody can see.
大家都看得出，這頭大象像條蛇。
A big earthquake occurred there last night,as/which was reported on TV.
據電視報道，昨夜那里發生了大地震。
She is from Shanghai,as/which I know from her accent.
她來自上海，那是我從她的口音知道的。
二、不同之處
1、as引導非限制性定語從句時，位置比較靈活，可位于主句之前，也可位于主句之中或之后;而which引導非限制定語從句只能位于主句之后，不能位于主句之前。如：
_______ is known to everybody,the moon travels round the earth.
A.It B.As C.That D.Which
答案：B
_______ is mentioned above,the number of the students in senior high schools is increasing.
A.Which B.As C.That D.It
答案：B
Air,as we know,is a gas.眾所周知，空氣是一種氣體。
He is very careful,as his work shows.
他的工作表現表明他非常謹慎。
as引導非限制性定語從句常有“如同......那樣”的含義，因此在一些固定結構中，如：
as we know;as is known to all(眾所周知)
as we all can see(正如我們大家都能看到的那樣)
as has been said before/above(正如前面所述)
as might be imagined(可以想象得到)
as might be expected(正如所預料的那樣)
as is often the case(情況通常是這樣)
以上種種固定搭配，一般不能用which代替as。
2、搭配上，在由the same或such所修飾的名詞后通常用as作關系代詞引出非限制性定語從句。如：
I have got into the same trouble as he (has).
我遇到了與他一樣的麻煩。
I've never heard of such a moving story as he is telling.
我從未聽過像他講得那么有趣的故事。
3、which引導的從句在意義上相當于一個并列句，可以用and this代替，意思是“這件事”;as引導的從句主要起連接上下文的作用，表達說話人的觀點、看法，并指出主句內容的根據或出處等。如：
He sold his new car,which surprised me.
=He sold his new car,and this serprised me.
Einstein,as we know,is a famous scientist.
我們都知道，愛因斯坦是一位著名的科學家。
As is known to all,Taiwan is part of China.
眾所周知，臺灣是中國的一部分。
4、當which在從句中指代的是先行詞本身而不是主句時，不可用as代替which。如：
The peach tree,which I planted last year,has not borne any fruit.
這棵桃樹是我去年種下的，還沒有結出任何果實。
The book,which I bought yesterday,is very instructive.
我昨天買的這本書很有教育意義。
5、在從句中作主語時，which既可作系動詞be的主語，也可作實義動詞的主語，而as只可作系動詞be的主語。如：
He married her,which was nature.(可用as代替which)
他和她結婚了，這是很自然的事。
She met the boy,which delighted her.(不可用as代替which)
她見到了那個男孩，這使得她很高興。
He failed in the exam again,which made his parents very angry.
他考試有不及格了，這是他父母很生氣。
6、as引導的從句在意義上不可與主語相悖，而which引導的從句則不受此限制。
Mum treats me like a baby,which I can't bear.
媽媽把我當小孩看待，這是我不能忍受的。
只用as而不用which：
一、當定語從句置于主句前面時：
例：As you see, the Chinese people are hard-working. (定語從句在句首)
你知道，中國人民是勤勞的。
注意下面句子的多種表達方法：
眾所周知，月球每月繞地球轉一圈。
1.As is known to everybody, the moon travels round the earth once every month.
2. The moon travels round the earth once every month, as/which is known to everybody.
3. It is known to everybody that the moon travels round the earth once every month.
4.What is known to everybody is that the earth travels round the earth once every month.
(后兩句屬名詞性從句范疇)
二、先行詞做主語且定語從句為被動語態時：
此時，從句謂語通常為： be known, be said, be reported， be announced, be mentioned等。如果從句是主動語態，一般用which作主語。
例1：She has been absent again, as is expected.
她又缺席了，這在預料之中。
例2：Tom has made rapid progress, which makes me very happy.
湯姆進步很快，這使我很高興。
另外，as常用在下列習慣用語中：as (it) seems likely, as (it) often happens, as (it) was printed out, as (it) was said earlier, as I remember (it), as I understand (it), as (it) appears, as it often the case, as anybody can see, as we have expected.
例1：Jack has won the first prize, as it often happens.
像往常一樣，杰克得了一等獎。
例2：She has read widely in Romantic Literature, as it appearsfromher essay ·
她廣泛涉獵了浪漫主義文學，這從她的文章中可以看出來。
只用which而不用as
一、關系代詞代替前面主句中的賓語從句或定語從句的謂語動詞后有復合賓語時：
例：I don't think that he will come to see me, which makes me sad.
我認為他不會來看我了，這使我傷心。
二、which一般用作實義動詞的主語，這時它所引導的從句與主句之間存在著邏輯上的因果關系時：
例：Tom was late for school again and again, which made his teacher very angry.
湯姆一次又一次上學遲到，這使得他的老師很生氣。
三、當非限制性定語從句是否定句時：
例：He pretended not to know me, which I didn't understand.
他假裝不認識我，我真不明白。
四、非限制性定語從句中的be動詞不能省略時，用which反之用as.
例1：Jane told me she won the match, which was a lie.
簡告訴我她贏了這場比賽，這是謊話。(was不可省略)
例2：As (was) planned, we met at the airport.
按照計劃，我們在機場相見了。(was可省略)
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