定语从句(Attributive Clauses)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。
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，在从句中所起作用如下：
Is he the man who/that wants to see you? 他就是想见你的人吗?(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 (of which) cover is green. 请递给我那本绿皮的书。
3)which, that
它们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在句中作宾语)
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)
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)when, where, why
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?
2)that代替关系副词
that可以用于表示时间、地点、方式、理由的名词后取代when, where, why和介词+ which引导的定语从句，在口语中that常被省略，例如：
His father died the year (that / when / in which) he was born. 他父亲在他出生那年逝世了。
He is unlikely to find the place (that / where / in which) he lived forty years ago. 他不大可能找到他四十年前居住过的地方。
一、疑问句中考查定语从句
1. Is this the farm ________ you visited last week?
A. where B. the one C. on which D. /
【解析】答案是D。命题人经常利用疑问句的特殊结构来干扰学生的正确选择。遇到这类定语从句时，最好的办法是先把疑问句还原成陈述句，然后判断谁是先行词，再看关系词在定语从句中所充当的成分，最后确定正确答案。
二、倒装句中考查定语从句
2. We came to a place， ________ stood a big tower.
A. which B. that C. / D. where
【解析】正确答案是D。为了保持句子平衡，句子用了倒装语序。倒装的使用使定语从句的结构变得较为特殊，因此对于使用倒装语序的定语从句，应先把倒装语序还原成正常语序，这样句子结构就比较清晰了。
三、 拆分词组和固定搭配
3. The second is connected with the use ________ the body makes of food.
A. of which B. where C. to do D. that
4. Why cant you realize the part ________ they have played in our life?
A. which B. on which C. when D. where
【解析】正确答案分别是D和A。一些词组和搭配被拆开后，句子的含义就变得难以理解。首先把拆开的词组复原是理解此类定语从句的关键。上述句子中包含以下词组：make use of， play a part (in)。
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四、添加插入语或状语
5. The scientist has made another discovery， _______ I believe is of great importance.
A. that B. / C. which D. why
【解析】应选择C。这类句子主要利用插入语或状语的添加来增加试题的难度。常见的插入语有：I think (suppose， expect， believe， imagine)， in my opinion， to tell you the truth等。做这类题目时，最佳的办法是先删去插入语或状语，这样句子的主干部分就一目了然了。
五、插入非谓语动词
6. Is this the man ________ you want to have ________
the radio for me?
A. who;repaired B. that;repaired
C. whom;repairing D. that;repair
【解析】D项正确。非谓语动词是英语中难度较大的语法项目之一，因而在定语从句中加入非谓语动词就成了学生最易失分的题目。对付这类题目最有效的办法就是将句子还原。如：我们可以把几个句子中的定语从句进行还原，还原后的句子应是：You want to have the man repair the radio for me.