定语从句的概念及用法是什么
定语从句的概念
定语从句是由关系代词和关系副词引导的从句，其作用是作定语修饰主句的某个成分，定语从句分为限定性和非限定性从句两种。状语从句分为时间状语从句，结果状语从句，让步状语从句，原因状语从句，条件状语从句以及行为方式状语从句。名词从句包括主语从句，宾语从句，表语从句和同位语从句及there be句型。综合素质评价
定语从句用法
在复合句中，修饰名词或代词的从句叫定语从句，被修饰的名词或代词叫先行词，引导定语从句的.有关系代词who,whom,who,which,that等和关系副词where,when,why等，关系代词和关系副词在定语从句中担任句子成份。
1.由who引导的定语从句中，who用作主语，如：This is the boy who often helps me.
2.由whom引导的定语从句中，whom用作宾语，如：The man whom you are waiting for has gone home.
3.由who引导的定语从句中，who用作定语，如：Do you know the girl who skirt is white?
4.由which引导的定语从句中，which用作主语或谓语动词的宾语或介词的宾语，如：
The room in which there is a machine is a work shop.
The river which is in front of my hou is very clean.
This is the pen which you want.水源保护区
注意：
(1)whom,which用作介词宾语时，介词可放在whom、which之前，也可放在从句原来的位置上;但在含有介词的动词固定词组中，介词只能放在原来的位置上。如：He is the very person whom we must take good care of.
(2)引导非限制性定语从句时，必须用关系代词which，不用that,如：I have lost
柯基的智商
my bag,which I like very much.
(3)关系代词在句中作主语时，从句的谓语动词的人称和数必须和先行词保持一致。
形容担心的成语 5.由that引导的定语从句中，that可以指人或物，在从句中作主语或谓语动词的宾语，但不能放在介词后面作介词宾语，如：
The book that I bought yesterday was written by Lu Xun.?
注意在下面几种情况下必须用that引导定语从句。
(1)先行词是不定代词all,few,little,much,something,nothing,anything等，如：
All that we have to do is to practi English.
(2)先行词被序数词或形容词最高级所修饰，如
The first letter that I got from him will be kept.
(3)先行词被all,any,every,each,few,little,no,some等修饰，如
I've eaten up all the food that you gave me.
(4)先行词被the only,the very,the same,the last修饰时如
He is the only person that I want to talk with.
中国综合社会调查
(5)先行词既有人又有物时，如:
They talked about persons and things that they met.
(6)当句中已有who时，为避免重复，如：Who is the man that is giving us the
class?
6.由when,where,why引导的定语从句，如:
I don't know the reason why he was late.
This is the place where we have lived for 5 years.
I'll never forget the day when I met Mr Li for the first time.
注意：先行词是表示地点时，如果从句的谓语动词是及物的，就用that(which)，如果从句的谓语动词是不及物的，就用where引导。This is the hou Which/that he has lived in for 15 years.(Where he has lived for 15 year.)
7.限制性定语从句和非限制性定语从句
(1)限制性定语从句是句中不可缺少的组成部分，主句和从句之间不用逗号分开。引导非限制性定语从句的关系代词有who,whom,who,which,of which等，这些关系代词都不能省略。
(2)非限制性定语从句是对主句先行词的补充说明，没有这种从句，不影响主句意思的完整，一般用逗号把主句和从句分开，关系代词用which,不用that;指人时可用who,如：I have two brothers,who are both students.
女人的比比
8.如何简化定语从句
(1).定语从句简化为形容词或形容词短语作后置定语。如:
My grandfather lives in a village that is far away from here.
→My grandfather lives in a village far away from here.我祖父住在离这儿很远的一个村子。男枪打野出装
This is a book that is worth reading.
→This is a book worth reading.这是一本值得看的书。
(2)定语从句简化为现在分词或现在分词短语作前置或后置定语。
The man who is standing under the tree is our English teacher.
→The man standing under the tree is our English teacher.
站在树下面的那个人是我们的英语老师。
I saw the hou that was burning at that time.→I saw the burning hou at that time.
当时我看到那房子在燃烧。
(3)定语从句简化为过去分词短语作后置定语。
I like to e the films which are directed by Zhang Yimou.→I like to e the films directed by Zhang Yimou.我喜欢看张艺谋导演的电影。
She is the girl who was praid at the school meeting.→She is the girl praid at the school meeting.她就是在校会上受表彰的那个女孩。
(4)定语从句简化为不定式作后置定语。
He is always the first person that comes to school.→He is always the first person to come to school.他总是第一个到校。
The report which will be given tomorrow is important to us.→The report to be given tomorrow is important to us.明天要作的报告对我们很重要。
(5)定语从句简化为what从句。
I couldn't remember the words that he said.→I couldn't remember what he said.
我记不得他说的话。
定语从句结构
定语从句公式
定语从句=先行词+关系词+从句
先行词
指被定语从句修饰的名词、代词或句子。
一般先行词出现在定语从句的前面。
关系词气上
关系词常有3个作用：
①连接作用，连接主句和定语从句。
②指代先行词。
③在定语从句中担当成分。
注：关系代词有主语、宾语、定语之分。一般who做主语或其宾格形式的whom做宾语(whom作宾语时可省略)，who作为定语(who不可省略)。关系代词在从句中作主语，宾语，定语等，关系副词在从句中作地点状语(where)，时间状语(when)，原因状语(why)。
定语
定语用来限定、修饰名词或代词，是对名词或代词起修饰、限定作用的词、短语(动词不定式短语、动名词表示的)汉语中常用“……的”表示。主要由形容词担任，此外，名词、代词、数词、分词、副词、不定式以及介词短语也可以来担任，也可以由一个句子来担任。单词作定语时通常放在它所修饰的词之前，作前置定语。短语、从句作定语时则放在所修饰的词之后，作后置定语。
被定语从句修饰的名词、代词称为先行词。如“the girl”，“the book”
如:She is the girl who likes singing. 她就是那个喜欢唱歌的女孩。
