as作定語從句
as和which都能引導定語從句,并都可以在定語從句中做主語或賓語,代表前面整個句子.以下是小編為大家整理分享的as作定語從句，歡迎閱讀參考。
as作定語從句
透析which與as在定語從句中的運用
定語從句是高中英語的主要語法項目之一,也是高考英語的常考知識點,尤其是as和which引導的定語從句,更是歷年高考試題中的重點和熱點.as和which在引導定語從句時既有相同點又存在著很大的區別.
一、相同點
1. as和which都能引導定語從句,并都可以在定語從句中做主語或賓語,代表前面整個句子.
例 1 He married her, as / which was natural. 他跟她結婚了,這是很自然的事.
例 2 He is honest, as we can see. 他很誠實, 這一點我們看得出來.(表示人們從日常主觀常識, 經驗對某一事情的看法、評價,用as為妥.)
2. 當非限定性定語從句置于句末時,as和which都可用來引導這個定語從句.
例 3 The number of senior high school students is increasing, as is mentioned above. （as引導非限定性定語從句,意思是“正如”.此時也可以換用which引導,但意思有別,意思是：“這一點上面提到了”.）
二、不同點
（一）語義上的區別
as作為關系代詞仍多少保留 “理由”“比較” “方式” “等同”等意義,而which沒有這些意義.因此,由as引導的定語從句通常在意義上不可與主句相悖,而且一般是肯定的,對主句意義起相輔作用,表示 “正如”等意義；而which引導從句則不受此限制.
例 4 Mother treats me just like a baby,which I can’t bear． 媽媽對我就像小孩,我真受不了.
例 5 She has married again,which was unexpected． 她又結婚了,這是大家沒有預料到的.
上面兩句中的which都不宜用as.
但當否定的定語從句作正面理解,對主句起相輔作用而不是與其相悖時,仍可用as.
例 6 He turned his eyes on Philip’s face,as he had not done for ten years．他轉過身來看著菲利普的臉,他十年來沒有這樣看過他的臉了.
例 7 He really can’t lend you the money,as you might not realize． 他的確不能把那些錢借給你,這一點你可能意識不到.
（二）用法上的區別
1. which與as引導非限制性定語從句的區別：
（1）which只能放在主句后面,而as引導的從句位置相對比較靈活,可以放在前,也可以放在后,甚至還可以分割主句.另外,as 常常有“正如、正像”的含義.
例 8 As he realized, I was very useful to him.（在前）
例 9 Air, as we know, is a gas. （在中）
例 10 He was a foreigner, as I know from his accent. (在后)
例 11 He came late again, which made his boss angry.（在后）
例 12 As is known to all, China is a developing country. 眾所周知,中國是發展中國家.
（2）在which引導的.定語從句中,謂語動詞若是am, is, are,則這些系動詞不能省略,而as后面若是這種情況,則可以省略.
例 13 He is a teacher, as (is) clear from his manner. (is可以省略)
例 14 He said he had never seen her before, which was not true. （was 不可省略）
（3）當which引導的從句在意義上近乎并列關系時,可以用and this, and that代替,意思是“這件事”.
例 15 He changed his mind, which(and this, and that) made me very angry. 他改變了主意,這使我很生氣.
而as主要起與上下文連接的作用,表達說話人的看法、觀點,并指出主句內容的出處或根據等.
例 16 Einstein, as we know, is a famous scientist.愛因斯坦,眾所周知,是一位偉大的科學家.
例 17 As is announced in today’s newspaper, we must improve our style of work. 今天的報紙上說,我們必須改進工作作風.
（4）做主語時,which既可以作系動詞be的主語,也可以作實義動詞的主語,而這時as 只可以做系動詞be的主語.
例 18 He married her, which was natural. （可用as代替which）他和她結婚,這是很自然的事.
例 19 He won a /the Nobel Prize in chemistry, which made him illustrious. (不可用as代替which)他獲得了諾貝爾化學獎,這使他名揚天下.
（5）當定語從句位于主句之后,純粹表示主句所述的內容,不帶有“如……那樣”的意思時,往往用which, 而不用as.
例 20 They were invited to the state banquet, which(as) was a great honor to them. 他們被邀請參加國宴,這對他們來說是莫大的榮幸.
例 21 We had to sleep in our wet clothes, which was most uncomfortable. 我們不得不穿著濕衣服睡覺,這簡直太不舒服了.
（6）當定語從句有“如同……那樣”的含義時,用as比用which更常見,而這些從句幾乎成為固定說法.
例 22 Things will turn out contrary to one’s wishes, as is often the case. 事與愿違,這是常有的事.
例 23 As was natural, this inordinate hope was followed by an excessive depression.這種過分希望之后,接著是極度的沮喪,是很自然的事.
例 24 The material is elastic, as is show in the figure. 這種材料有彈性,如圖所示.
例 25 As we know. 眾所周知.
例 26 As has been said above/ before. 正如前文所述 .
（7）當定語從句的關系代詞指的是先行詞本身時,只能用which.
例 27 These apple trees, which I planted tree years ago, have not borne any fruit.這些蘋果樹是我三年前種下的,沒結出任何果實.
例 28 The Thames, which is now clean enough to swim in, was polluted for over a hundred years.泰晤士河,現在已經很干凈,可以在里面游泳,它曾被污染了一百多年.
（8）帶介詞的典型的定語從句,必須用which,不能用as.
例 29 There is a great deal of oxygen around us, without which we could not live. 我們周圍有許多氧氣,沒有它我們就無法生存.
例 30 The shed in our garden, in which we often played, has lasted for a long time. 我們經常玩耍的花園里的那個棚子,已經有很長時間了.
（9）as常與從句中的know,see, hear,expect等動詞連用,也常用于as often happens,as is often the case（常有的事）等句子中；而which一般不用于以上情況.
例 31 As is well known,Shanghai is a big city．
（10）當后置的非限制性定語從句是否定結構時,只能用which引導.
例 32 The result of the experiment was very good, which we hadn’t expected.
2. 引導限制性定語從句時which與as的區別：
(1)先行詞如果是表示物的名詞或代詞,在從句中又做介詞的賓語時,只能用which.
例 33 This is the pan in which I boiled the milk. 這就是我煮牛奶的鍋.
（2）前面有as時,引導定語從句的關系代詞用as, 不用which.
例 34 There are as many dictionaries as are needed.所需要的字典都有了.
（3）前面有such時,引導的定語從句的關系代詞用as, 不用which.
例 35 Such women as know Tom thought he was charming. 認識湯姆的女人都認為他很迷人.
例 36 I have never heard such stories as he tells. 他講的那些故事我從沒聽過.
（4）前面有the same時,引導定語從句的關系代詞用as而不用which.
例 37 We are facing the same problems as we did years ago.我們正面臨著和多年以前同樣的困難.
例 38 This is the same wallet as I lost. 這只錢包與我丟失的那只相同.
（5）單個詞引導限制性定語從句時,一般不用as而用which和that.由于關系詞在從句中作賓語,which和that都可以省略.
例 39 The project which/that a British businessman has invested in is under construction at present.
（6）“介詞+關系代詞”引導定語從句時,只能用which.
例 40 Recently I bought an ancient Chinese vase, the price of which was very reasonable.
注：此時的which不能用as來代替.另外還應注意：引導定語從句時,which不能單獨作定語,此時不管先行詞是人還是物,都只能用whose引導,但指物時,可以用of which替換.
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