as引導的定語從句的用法
ove, as is often the case, as/indeed it is
例:As is well known，great changes have taken place in China. 或Great changes, as is well known, have taken place in China.眾所周知，中國發生了巨大的變化。( as在定語從句中作主語。)
This experiment is very simple，as indeed it is.實驗非常簡單，事實上也確實如此。(as在定語從句中作表語。)
注意：① which在引導非限制性定語從句時，也有和as一樣的功能，可以代替整個句子，但which只能用在主句之後。
②在as所引導的非限制性定語從句中，如果運用的是被動語態結構，be動詞可以省略；但which沒有此用法，be動詞不可省。例如:She married him，which was unexpected.＝She married him as（was） unexpected.她嫁給了她，這一點大家都沒有料到。（作主語，代替前面的句子；用which時was不可省。）
二 as除了代替整個句子，也可以代替主句中一個特定的詞。as在它引導的定語從句（限制性或非限制性）中可以充當主語，賓語和表語；在這種用法中它經常和such, so, the same等詞搭配使用；且當先行詞中有such, so, the same等詞修飾時，關係代詞通常必須用as。
例如:1. They were satisfied with this decision，as was agreed beforehand.他們對這個決定都滿意，這事先已經經過他們同意了。( as在定語從句中作主語，其先行詞是this decision)
2. I never heard such stories as he tells.我從未聽過他講的這類故事。( as在定語從句中作賓語，先行詞是such stories.)
place doesn't look the same as it was before liberation.這個地方看上一去和解放前大不一樣了。( as在定語從句中作表語，先行詞是same)
you bought the same book as I referred to yesterday?你有沒有買我昨天説的那本書啊？( as在定語從句中作賓語，先行詞是book)
注意:先行詞中有the same修飾時，定語從句也可用that引導，但意思上有區別，as表示與此同類； that表示就是那一個，同物。
例如:Have you brought the same book that I gave you yesterday?
你有沒有把我昨天給你的那本書帶來啊？( that在定語從句中作賓語，先行詞是book。體會：本句中所指的書是同一本，上句中指的是同一類書，而並不就是那一本。)
介詞+關係詞怎麼用？介詞加關係詞分別等於什麼？
答：一、“介詞＋關係代詞”的用法
當關系代詞在定語從句中作介詞賓語時，我們通常用“介詞＋關係代詞”引導定語從句。如果指“人”，用“介詞＋whom”；如果指“物”，用“介詞＋which”。例如：
Do you know the lady with whom our manager is talking in the office? Where is the supermarket in which you bought the laptop last week? ●使用“介詞＋關係代詞”要注意以下幾點：
(一)選用介詞的依據：
(1) 根據定語從句中謂語動詞的搭配習慣(即固定短語)。例如：
Yesterday we visited the West Lake for which Hangzhou is famous.
(2) 根據先行詞的搭配習慣(約定俗成，不一定是短語)。例如：
The old woman with whom you talked just now is a famous artist.
(3) 根據句子的意思來選擇。例如：
The naughty boy made a hole in the wall through which he could see what is happening outside.
(4) 表示“所有”關係或“整體中的一部分”時，通常用介詞of。例如： I have about 20 books, half of which were written by Bing Xin, the famous writer.
(二)在定語從句中，含介詞的短語動詞不可拆開使用(短語拆開後含義發生變化)，如look after, look for等。例如：
The babies whom the nurses are looking after are very healthy.(正) The babies after whom the nurses are looking are very healthy.(誤)
(三)“of which / whom”有時可以用“whose＋名詞”結構來改寫。例如： The building whose roof was damaged in the earthquake has been
repaired.
＝The building of which the roof was damaged in the earthquake has been repaired.
(四)當先行詞為way並且定語從句中缺少狀語時，通常用in which或that引導定語從句(in which或that可省略)；如果定語從句中不缺少狀語，則用關係代詞引導(that 或which 可省略)。例如：
All of us disliked the way(in which / that)Tom settled the maths problem.
I don’t understand the way(that/which)the teacher explained to me.
(五)in that不可以引導定語從句，但可以引導原因狀語從句。例如：
She didn’t attend the meeting in that / because she was seriously ill.
二、“介詞＋關係代詞”與關係副詞的.轉化
(1)當先行詞表示地點，定語從句中缺少地點狀語時，通常用關係副詞where引導，此時也可選用表示地點的介詞＋which來代替關係副詞where。例如：
I visited the village where many children couldn’t go to school because of poverty.
＝I visited the village in which many children couldn’t go to school because of poverty.
(2) 當先行詞表示時間，定語從句中缺少時間狀語時，通常用關係副詞when引導，此時也可選用表示時間的介詞＋which來代替關係副詞when。例如：
We’d better fix a date when we will practice speaking English next week.
＝We’d better fix a date on which we will practice speaking English next week.
(3) 當先行詞為reason，定語從句中缺少表示原因狀語時，通常用關係副詞why引導，此時也可以用for which來代替關係副詞why。例如：
Can you tell me the reason why you were late for school?
＝Can you tell me the reason for which you were late for school? 介詞+關係代詞”引導的定語從句
由“介詞+關係代詞”引導的定語從句主要用於正式文體中，這兒的關係代詞主要是which和whom，介詞的選用要根據句意或一些固定搭配來確定。
“介詞+關係代詞”(關係代詞一般指的是which/whom)引導的定語從句，有以下幾種情況:
1.“介詞+which”在定語從句中作時間地點原因狀語，相當於關係副詞。如:
(1)This is the reason for which(=why) he left the company. 這就是他離開公司的原因。
(2)He will never forget the day on which (=when) he went there. 他永遠忘不了去那兒的那一天。
(3)Is this company the one in which (=where) you worked half a year ago?這就是半年前你在那兒工作的公司嗎?
2.“介詞+which/whom”在定語從句中作目的方式狀語。如:
(1)Can you tell me for whom you are working?
你能告訴我你現在為誰工作嗎?
(2)There is a big hole on the wall through which he can see what’s happening inside.
牆上有一個大洞，通過這個洞他能看到裏面所發生的一切。
(3)The train by which he is travelling is arriving.
他乘坐的那輛火車就要到了。
(4)In the dark street， there wasn’t a single person to whom she could turn for help.在漆黑的街上，沒有一個人她可以求助。
3.“不定代詞數詞或名詞+of which/whom”在定語從句中充當主
語。如:
(1)There are sixty students in our class， all of whom are working hard.
班上有60 名學生，他們都在努力學習。
(2)He paid the boy ten yuan for cleaning the windows， most of which hadn’t been cleaned for at least a year.
他給了那個男孩十元錢擦那些至少一年未擦的窗户。
4.“形容詞最高級+介詞+關係代詞”在定語從句中充當主語。如:
(1)There are sixty students in the class， the tallest of whom is Li Ming. 班上有六十名學生，其中最高的是李明。
(2)There are seven continents in the world， the largest of which is Asia. 全球有七大洲，最大的是亞洲。
5.“the+n.+of+which”引導的定語從句，相當於whose引導的定語從句。如:
(1)We took a photo of a rocket， the length of which was about 30 meters.=We took a photo of a rocket， whose length was about 30 meters. 我們給火箭拍了照，火箭大約長30米。
(2)Recently I bought an ancient Chinese vase， the price of which was very reasonable.=Recently I bought an ancient Chinese vase， whose price was very reasonable.
最近我買了一箇中國古代花瓶，價格非常合理。
6.“介詞+whose”修飾後面的名詞。如:
He is the very man in whose pocket I found my lost money.
他就是那個我在他的口袋裏找出我丟掉的錢的人。
7.“介詞+which+不定式”此結構相當於一個簡化了的定語從句。如:
(1)He found something about which to write(=he could write). 他發現有些事是可以寫的。
(2)The poor man has no house in which to live.=The poor man has no house in which he can live. 這個窮人沒有房子住。
8.介詞的選用要根據句意或一些固定搭配決定。其中的介詞可以是in， on， about， from， for， with， at， of， without， to。如:
(1)Galilia built a telescope through which he could study the sky. 伽利略建起了望遠鏡，通過望遠鏡他可以研究天空。
(2)The cloth of which this coat is made is produced in Shanghai. 這件外套的布料是由上海製造的。
(3)He wrote many articles in which he expressed his love for
his motherland.
他寫了許多文章，在文章中他表達了對祖國的熱愛。
但有些含介詞的短語動詞一般不能拆開，介詞仍放在動詞的後面。
如:listen to， depend on， take care of， pay attention to， look at等。
This is the boy whom she has taken care of.
這就是那個她照顧的非常好的男孩。
That is a problem we should pay close attention to.
這是一個我們應該密切關注的問題。
強調句與定語從句的區別是：在定語從句中一般使用關係代詞that, which，who, whom或關係副詞when, where，why等,先行詞(中心詞)一般是名詞或名詞短語，而在強調句中，可以用副詞、介詞短語或從句來作被強調的內容。；而在強調句中則主要使用that，who；
有時強調句在形式上和定語從句、狀語從句很相似。我們除了從意思上進行區分外，還能根據強調句的結構特點來進行判斷，如能去掉It ...後，句子仍然通順，就是強調句。這一點很重要.
試比較：
①It is a question that needs careful consideration.
②It is novels that Miss Williams enjoys reading.
簡析：句①是含有定語從句的句子，在此It是指示代詞，It is a question是個"主語+系動詞+表語"結構，如果去掉It ,句子結構就不完整了。句②是強調句，在此It是個引導詞，沒有具體含義，如果去掉It ，把語序稍加調整，句子結構仍然是完整的。
區分定語從句與強調句 區分定語從句和強調句可用還原法，因為強調句的基本句式為 It is (was)+被強調部分+that+句子的其餘部分，因此只需將it is(was) 後面的部分還原到原來的句子中，如果成份完整，則為強調句，如果成份不完整則為定語從句。
1) It is this street _______I happened to meet him.
It is in this street _______I happened to meet him.
A．that
B．where
C．which
D．from which 首先，我們看到主句部分為 it is結構，可能是定語從句可能是強調句，利用還原法，將兩部分分別還原，得出1．I happened to meet him this street. 2．I happened to meet him in this street. 1句子成份不完整，為定語從句，用where；2句子成份完整為強調句，選that。
2) Where did you meet him?
It is in the cinema_______ I met him.
It is in the cinema_______ door faces west.
A．that
B．where
C．whose
D．which 仍然採取還原法，得出1．I met him in the cinema. 2．Door faces west in the cinema. 1句子成份完整，確定為強調句，用that選A；2明顯不是一個意思表達清楚的句子，其實本句是一個省略句，全句為：It is in the cinema _______door faces west that I met him. 強調句部分已經省略，而句中door faces west 是一個定語從句，表示門朝西開的電影院，因此選C，whose 在做題中我們經常可以看見帶有定語從句的強調句，這時仍可用還原法加以辨別：(1) Was it in the cinema _______Smith met you _______you saw the film?
A．that, that B．whom, then C．where, that D．which, where (C) (2) Where did you found XingMing? It was in the office _______he worked. A．this B．which
在定語從句中one of 後的先行詞若是可數名詞的複數，謂語動詞就用複數形式，the only one of 後的謂語動詞用的是單數形式。
e.g. Tom is one of the boy students in our class who are often late. Tom is the only one of the boy students in our class who is often late.
5. 代詞/名詞＋ 定語從句，從句謂語動詞的單複數與所修飾的詞一致。 I , who am wrong, should apologize to him. 我錯了，應該向他道歉。
She came across a former classmate who is very wealthy.
注意：在“ one of +複數名詞＋定語從句”，定語從句一般看作修飾複數名
詞，從句中的謂語動詞用複數；在“the only one of＋複數名詞＋定語
從句”結構中，定語從句應視為修飾單數名詞，從句謂語動詞用單數。 This is one of those cars that were damaged in the accident.
這是事故中被損壞的車中之一。
She is the only one of the girls who is interested in literature.
她是這些人中唯一喜歡文學的女孩。
