定于从句是高中重点知识，也是高考常考点，大家也不容易掌握，这篇文章主要教你关系代词引导的定语从句
　关系副词引导的定语从句 判断关系代词与关系副词 限制性和非限制性定语从句等内容，有例题讲解
定语从句在句中做定语，修饰一个名词或代词，被修饰的名词词组或代词即先行词。定语从句通常
出现在先行词之后，由关系词（关系代词或关系副词）引出。
关系代词有：who, whom, whose, that, which等。
关系副词有：when, where, why等。

18.1 关系代词引导的定语从句
　　关系代词所代替的先行词是人或物的名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。
1）who, whom, that
　 这些词代替的先行词是人的名词或代词，在从句中作主语和宾语。例如：
　 Is he the man who/that wants to see you? 他就是你想见的人吗？（who/that在从句中作主语）
　 He is the man whom/ that I saw yesterday. 他就是我昨天见的那个人。（whom/that在从句中作宾语）
2） whose 用来指人或物，（只用作定语, 若指物，它还可以同of which互换）。例如：
They rushed over to help the man whose car had broken down.　那人车坏了，大家都跑过去帮忙。
Please pass me the book whose cover is green.　请递给我那本绿皮的书。

Please pass me the book of which the cover is green.　请递给我那本绿皮的书。
3）which, that所代替的先行词是事物的名词或代词，在从句中可作主语、宾语等。例如：
A prosperity which / that had never been seen before appears in the countryside.
农村出现了前所未有的繁荣。（which / that在句中作主语）
The package （which / that）you are carrying is about to come unwrapped. 你拿的包快散了。（which / that在句中作宾语）

18.2 关系副词引导的定语从句
　 关系副词可代替的先行词是时间、地点或理由的名词，在从句中作状语。
1）关系副词when, where, why的含义相当于\"介词+ which\"结构，因此常常和\"介词+ which\"结构交替使用。例如：
　 There are occasions when （on which） one must yield.　任何人都有不得不屈服的时候。
　 Beijing is the place where（in which） I was born.　北京是我的出生地。
　 Is this the reason why （for which） he refused our offer?　这就是他拒绝我们帮助他的理由吗？

18.3 判断关系代词与关系副词
　 方法一： 用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。例如：
　 This is the mountain village where I stayed last year. 这是我去年呆过的山村。
　 I\'ll never forget the days when I worked together with you.我永远不会忘记与你共事的日子。
　 判断改错：
　 （ × ） This is the mountain village where I visited last year.
　 （ × ） I will never forget the days when I spent in the countryside.
　 （ √ ） This is the mountain village （which） I visited last year.
　 （  √） I'll never forget the days （which） I spent in the countryside.
　　习惯上总把表地点或时间的名词与关系副词 where, when联系在一起。此两题错在关系词的误用上。
　 方法二： 准确判断先行词在定语从句中的成分（主、谓、宾、定、状），也能正确选择出关系代词/关系副词。
例1. Is this museum ___ you visited a few days age? A. where　B. that　 C. on which　 D. the one
例2. Is this the museum ____ the exhibition was held. A. where　B. that　 C. on which　　D. the one
答案：例1 D，例2 A
例1变为肯定句： This museum is ___ you visited a few days ago.
例2变为肯定句： This is the museum ___ the exhibition was held.
　　在句1中，所缺部分为宾语，而where, that, on which都不能起到宾语的作用，只有the one既做了主句的表语，又可做从句的宾语，可以省略关系代词，所以应选D。
　　而句2中, 主、谓、宾俱全，从句部分为句子的状语表地点，既可用副词where，又因 in the museum词组，可用介词in + which 引导地点状语。而此题中，介词on 用的不对，所以选A。
　　关系词的选择依据在从句中所做的成分，先行词在从句中做主、定、宾语时，选择关系代词（who, whom, that, which, whose）； 先行词在从句中做状语时，应选择关系副词 （ where 地点状语，when 时间状语，why 原因状语） 。

18.4 限制性和非限制性定语从句
1） 定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开。例如：
This is the house which we bought last month. 这是我们上个月买的那幢房子。（限制性）
The house, which we bought last month, is very nice. 这幢房子很漂亮，是我们上个月买的。（非限制性）
2） 当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的。例如：
Charles Smith, who was my former teacher, retired last year. 查理?史密斯去年退休了，他曾经是我的老师。
My house, which I bought last year, has got a lovely garden.　我去年买的的那幢房子带着个漂亮的花园。
This novel, which I have read three times, is very touching. 这本小说很动人，我已经读了三遍。
3） 非限制性定语从句还能将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数。例如：
He seems not to have grasped what I meant, which greatly upsets me. 他似乎没抓住我的意思，这使我心烦。
Liquid water changes to vapor, which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。
说明：关系代词that和关系副词why不能引导非限制性定语从句。

18.5 介词+关系词
1）介词后面的关系词不能省略。
2）that前不能有介词。
3）某些在从句中充当时间，地点或原因状语的\"介词+关系词"结构可以同关系副词when 和where 互换。有时，前面的介词可移到定语从句的中间或后面，此时whom可用who, that代替；which可以用that代替。而且who, whom, which, that都可省略。例如：
This is the house in which I lived two years ago. 这是我两年前住过的房子。
This is the house where I lived two years ago.

This is the house which/that I lived in two years ago.
Do you remember the day on which you joined our club? 还记得你加入我们俱乐部的那一天吗？
Do you remember the day when you joined our club?

介词+which+n.的用法，常见的如： in which case/at which time/in which way…实际上相当于and in that case/and at that time/and in that way…

She may be late, in which case we ought to wait for her. 她可能迟到，因此我们应该等她。

I will be around the area at 5 pm, at which time I'll pick you up.

from where 的用法
  from where实际上属于“介词+副词”结构，但也可以引导定语从句，表示“从那里”，如：
He stood behind the curtain, from where he could see what was happening outside.他站在窗帘后面，从那里他可以看到外面正在发生的事。

18.6 as, which 非限定性定语从句
　　由as, which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。由as, which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。区别如下：
一、 as 引导非限制性定语从句，可放在主句之前，或者主句之后，甚至可以切割一个主句；which引导的非限制性定语从句只能放在主句之后。另外，as有“正如……，正像……”的意思；如：
(1) As is known to all, China is a developing country.
(2) He is from the south, as we can see from his accent.
(3) John, as you know, is a famous writer.                                                                                 
(4) He has been to Paris more than several times, which I don’t believe.
注意：当主句和从句存在逻辑上的因果关系时，常用which
(5) Tom was always late for school, which made his teacher angry.

二、 as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用which。
如：It rained hard yesterday, which prevented me from going to the park.
As is known to the world, china is great country.

三、as多用于固定搭配中：as is often the case(这是常有的事)，as was expected(不出所料)，as often happens(正如经常发生的那样)，as is known to all(众所周知)，as has been said before(如上所述)，as is mentioned above(正如上面所提到的)等。

四、如果非限制性定语从句部分是否定意义的句子，只能用which.

如：He should have passed the driving test, __________was beyond expectation.

    He passed the driving test,________was expected.
典型例题　
1）Alice received an invitation from her boss, ___came as a surprise. A. it　 B. that　 C. which　　D. he
　 答案C. 此为非限定性从句，不能用 that修饰，而用which.，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。
2）The weather turned out to be very good, ___ was more than we could expect.
A. what　B. which　C. that　D. it
　 答案B。which可代替句子，用于非限定性定语从句，而what不可。That 不能用于非限定性定语从句，it不为连词，使由逗号连接的两个句子并在一起在英语语法上行不通。
3）It rained hard yesterday, ____ prevented me from going to the park..
A. that　B. which　　C. as　 D. it
　 答案B. as 和which在引导非限制性定语从句时，这两个关系代词都指主句所表达的整个意思，且在定语从句中都可以作主语和宾语。但不同之处主要有两点：
（1）as 引导的定语从句可置于句首，而which不可。
（2） as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用which.。在本题中，prevent由于是行为动词，所以正确选项应为B。
as 的用法
例1. the same…as；such…as 中的as 是一种固定结构, 和……一样……。例如：
　　 I have got into the same trouble as he （has）. 我碰到了跟他一样的麻烦。
例2. as可引导非限制性从句，常带有\'正如\'。例如：
　　 As we know, smoking is harmful to one\'s health. 如我们所知，吸烟有害健康。
　　 As is known, smoking is harmful to one\'s health.
　 As是关系代词。例1中的as作know的宾语；例2中，它充当从句的主语，谓语动词know要用被动式。

18.7 先行词和关系词二合一
　1） Whoever spits in public will be punished here. （Whoever 可以用 anyone who 代替）
　2） The parents will use what they have to send their son to technical school.（what 可以用all that代替）

18.8 what/whatever; that/what; who/whoever
1）what = the thing which；whatever = anything。例如：
　　　What you want has been sent here. 你要的动词都送来了。
　　　Whatever you want makes no difference to me. 不管你要什么，跟我没什么关系。
2） who= the person that　 whoever= anyone who。例如：
　　 （ × ）Who breaks the law will be punished.
　　 （ ×）Whoever robbed the bank is not clear.
　　 （√）Whoever breaks the law will be punished. 王子犯法，与庶民同罪。
　　 （√ ）Who robbed the bank is not clear. 谁抢了银行还不清楚。
3） that 和 what　
　　当that引导定语从句时，通常用作关系代词，而引导名词性从句时，是个不充当任何成分的连接词。宾语从句和表语从句中的that常可省略。What只能引导名词性从句，用作连接代词，作从句的具体成分，且不能省略。例如：
　　I think（that）you will like the stamps. 我想你会喜欢这些邮票的。
　　What we need is more practice. 我们需要的是更多的实践。

18.9 关系代词that 的用法
1）不用that的情况
a） 引导非限定性定语从句时。例如： （错）The tree, that is four hundred years old, is very famous here.
b） 介词后不能用。例如：
We depend on the land from which we get our food. 我们依赖土地获得食物。
We depend on the land that/which we get our food from.
2） 只能用that作为定语从句的关系代词的情况
a）　在there be 句型中，只用that，不用which。
b）　在不定代词，如：anything, nothing, the one, all, much, few, any, little等作先行词时，只用that，不用which。
c）　先行词有the only, the very修饰时，只用that。　
d）　先行词为序数词、数词、形容词最高级时，只用that。.
e）　先行词既有人，又有物时。例如：
All that is needed is a supply of oil. 所需的只是供油问题。
Finally, the thief handed everything that he had stolen to the police. 那贼最终把偷的全部东西交给了警察。