初三英语定语从句讲解及练习题在复合句中修饰名词和代词的从句叫做定语从句。被定语从句修饰的名词或代词叫做先行词。
引导定语从句的关系代词有who, whose, whom, which, that 。
引导定语从句的关系副词有when, where, why。
关系代词在定语从句中做主语，宾语，定语。关系副词在定语从句中做状语。
一、who引导的定语从句,who在从句中做主语(口语中也可做宾语)，修饰表示人的先行词。
This is the man who helped me.
The boy who//whom we saw yesterday is John’s brother.
二、whom引导的定语从句,whom在从句中作宾语,修饰表示人的先行词，口语中可以省略。
The doctor (whom) you are looking for is in the room.
The person (whom) you just talked to is Mr. Li.
=The person to whom you just talked is Mr. Li. (介词后whom不能省略)
The babies whom the nurses are looking after are very healthy.
(固定短语中的介词一般不能拆开，仍放在动词之后。
look for / look after /take care of / put on / take off…)
三、whose引导的定语从句,whose在从句中作定语，修饰表示人或物的先行词。
Do you know the woman whose name is Mary. Pass me the dictionary whose cov er is black.
He has a friend whose father is a doctor.
四、that引导的定语从句，that在从句中做主语或宾语、修饰表示人或物的先行词。作宾语时可省略,不能放在介词后面作宾语. (that指人时，相当于who
或者whom；指物时，相当于which)
The letter (that//which) I received was from my father.
I can’t find the letter that//which came this morning.
Do you still remember the days (that//which)we spent together ?
This is the man that//who helped me.
The house (that//which) we live in is not large. =The house in which we live is not l arge.
The doctor (that//whom //who)you are looking for is in the room.
五、which引导的定语从句，which在从句中做主语，也可做宾语，或介词的宾语，修饰表示物的先行词。
This is the book (which/that ) you want.
The building which//that stands near the river is our school.
The room in which there is a machine is a workshop.(介词后面的which不能省略) The house (which/that) we live in is not large.
This is the watch (which/that ) he was looking for.
六、that 和which 都可以修饰表示物的先行词, 但是下列情况只能用that.①. 先行词为不定代词all, few, little, much, everything, nothing, anything等.
All (that) you have to do is to practise every day. There isn’t much (that) I can do.
Tell us everything that you know, please.
Is there anything that you don’t understand?
②. 先行词被序数词或形容词的最高级所修饰时.
The first lesson (that) I learned will never be forgotten.
This is the best film (that ) I have ever seen.
③. 先行词被all, any, every, few, little, no, some, much 等不定代词修饰时.
I have read all the books (that) you gave me.
④. 先行词被the only, the very, the last, the same 等修饰时.
This is the very book that I want to read.
This is the same book that I want to read.
This is the last time ( that ) I shall give you a lesson.
This is the only thing that I can remember.
七、由when 引导的定语从句，修饰表示时间的先行词，when为关系副词，做定语从句的时间状语。
I still remember the day when I first came to Beijing.
I still remember the day on which I first came to Beijing.
( 介词＋which可以代替when)
I’ll never forget the time when we worked on the farm.
I remember the days which//that we spent together.
八、由where 引导的定语从句，修饰表示地点的先行词，where为关系副词，做定语从句的地点状语。
This is the place where we lived for five years.
The factory where his father works is in the west of the city.
The factory in which his father works is in the west of the city.
( 介词＋which可以代替where)
This is a place which/that I wanted to visit.
Shanghai is the city where I was born.
九、Why引导的定语从句，why做原因状语。
I know the reason why he came late. ( for＋which可以代替why)
The reason why / for which he was late was that he was ill.
十、关系代词在从句中作主语，谓语动词的数与先行词保持一致。
The student who is good at English studies hard.
The students who are good at English study hard.
十一、定语从句可分为两大类，即限制性定语从句和非限制性定语从句。
①限制性定语从句是先行词在意义上不可缺少的定语，如果去掉的话，主句的意思就不完整，意义就表述不明。这种句型一般定语从句紧接先行词（不用逗号隔开）如：
I was the only person in my office who was invited.
②非限制性定语从句。它与主句的关系不十分密切，只是对先行词起补充、说明的作用，也就是说即便去掉定语从句，句意也不受影响。主从句之间常用逗号分开，且非限制性定语从句不能用that来引导。
This was the American Civil War, which lasted 4 years before the North won in t he end.
