C．why 指原因，在限制性定语从句中作原因状语。Please tell me the reason why you missed the plane. 请告诉我你误机的原因。(why = for which)Te reason why he was punished is unknown to us. 他受惩罚的原因我们都不知道。注意:无论是关系代词，还是关系副词，都在定语从句中取代了先行词，因此，先行词在定语从句中不复出现。【误】This is the book that I borrowed it yesterday.【正】This is the book that I borrowed yesterday. 这就是我昨天借的书。（that在定语从句中取代了先行词the book，作borowed的宾语，因此，要去掉it）【误】The English Corner is the place where people often go there to practise their spoken English.【正】The English Corner is the place where people often go to practise their spoken English. 英语角是人们经常去练习英语口语的地方。（where在定语从句中取代了先行词the pace，作go的状语，因此，要去掉there）
三、限制性定语从句和非限制性定语从句
根据定语从句在句中所起的作用，可分为限制性定语从句和非限制性定语从句两大类。
A．限制性定语从句限制性定语从句是先行词在意义上不可缺少的定语，用于修饰和限定先行词。如果去掉，主句的意思就不完整或失去意义。书写时不用逗号与先行词分开。This is the boy who broke the window.这就是打破窗子的孩子。（the boy是先行词，who broke the indow是限制性定语从句，明确指出the boy是打破窗子的那个孩子）I have a book which teaches English grammar. 我有一本讲解英语语法的书。（a book是先行词，which teaches English grammar是限制性定语从句，修饰the book）The people whom you met in the hall are from Japan. 你在大厅见到的那些人来自日本。（定语从句whom you met in the hall定先行词the people）
B．非限制性定语从句非限制性定语从句在意义上只是一个附加修饰语，对先行词或主句作些附加的说明。如果去掉，主句的意思仍然清楚。书写时往往用逗号与先行词分开。I, who am your friend, will share the work with you. 我是你的朋友，将与你分担这项工作。（I是先行词，who am your friend是非限制性定语从句，对先行词I起附加说明的作用）New Concept English is intended for foeign students, which is known to us all. 新概念英语是专为外国学生编写的，这是我们大家都知道的。（which is known to us all是非限制性定语从句，对主句作进一步的补充说明）
C．在下列情况下，通常使用非限制性定语从句。1．当先行词表示的是世界上独一无二的人或物时。The sun, which gives us light and heat, is a fixed star.太阳是一颗恒星，它给我们光和热。Last year I visted the Peoples Great Hall, where many important meetings are held every year. 去年我参观了人民大会堂，每年许多重要会议都要在那里举行。
2．当定语从句修饰整个主句时。Taiwan belongs to China, as everyone knows.众所周知，台湾属于中国的领土。The weather was very terrible, which we hadn expected. 天气非常糟糕，这点们没有料到。
3．当先行词是专有名词，或先行词本身指示意义十分明确时。Mr. Joe lives in Beijing now, which is quite a long way from here.乔先生现在住在北京，那里距离这儿很远。I congratulate my neighbour, whose son has just won the election.我祝贺我的邻居，他的儿子刚刚赢得选举。
四、关系代词和关系副词的选用
引导定语从句的关系代词和关系副词的选用，比较复杂除了牵涉到所指的先行词是人还是物，所引导的定语从句是限制性的还是非限制性的，以及关系词在从句中充当什么句子成份外，还要根据习惯用法而定。
A．只用who在下列情况下，一般不能用that代替who。1．在非限制定语从句中。
His mother, who loves him very much, is strict with him. 他妈妈十分地爱他，对他要求很严格。
3．先行词是one, anyone, those时。One who has nothing to fear for hiself dares to tell the truth. 一个无所畏惧的人敢说真话。Anyone who breaks the law shall be published. 任何犯法的人都将受到惩罚。Those who are against the plan put up your hands please. 凡是反对这项计划的人，请举手。
4．在therehere be开头的句子中。Here is a boy who wants to see you. 有个男孩想见你。
4．先词与定语从句被其他词所分隔时。Don tell anyone about the secret who oughtn to know. 不要把这秘密告诉任何一个不该知道它的人。I was the only person in my office who was invited.我是办公室里唯一受到邀请的人。
B．只用whichwhom在下列情况下，一般不能用that代替whichwhom。1．在非限制性定语从句中。The weather was very terrible, hich we hadn expected. 天气非常糟糕，这我们没有料到。
2．介词后面。关系代词紧跟在介词或短语介词后面，只能用which或whom，不能用that。He climbed up to the top of a large rock, from which he got a good view. 他爬到一块巨大的岩石顶上，从那里他看到很好的景色。（也可用from where）Sound is a tool, by means of which people communcate with each other. 声音是工具，人们通过这个工具进行交流。They asked me a lot of questions, most of which I couldn answer. 他们问了我许多问题，大部分我都不会回答。
C．只用that在下列情况下，限制性定语从句中一般只用that引导1．当先行词为everything, anything, nothing, all, none, few, little等词时，或当先行词被every, any, all,some, no, little, few, much等词修饰时。Everything that they said was true. 他所说的一切都是真的。He is dead and theres nothing that can be done. 他死了，再也没有什么办法了。There was little that we could do to help her. 我们没有什么能帮助她的。These walls are all that remain of the ancint city. 这些墙是这座古城所残存下来的全部。
提示：something 后面可用which引导定语从句。There is something(whichthat) Id like to tell you. 有些事我想告诉你。
2．当先行词被序数词或形容词最高级修饰时。The first place (that) they visited in London was the Big Ben. 在伦敦他们参观的第一个地方是大本钟。She was probably the hardest working student (that) I have ever taught. 她也许是我教学生中学习最勤奋的。
3．当先行词被the very, the only修饰时。This is the very grammar book (that) I want to buy. 这正是我要买的语法书。Beauty is the only thing (that) Emily can be proud of. 美丽是埃米莉唯一能骄傲的东西。
4．当先行词为who或前面有who, which等疑问代词时。Who that has common sense will believe uch nonsense 有常识的人谁会相信这种无聊的事情？Who is the man that is standing by the gate 站在门口的那个人是谁？Which is the T-shirt that fits me most 哪件T恤衫最合我的身？
提示：关系词在定语从句中有三大作用1. 连接作用——连接先行词和定语从句。I gave her all the money that I had. 我把我所有的钱都给了她。（that 连接先特词money和定语从句I had）
2. 替代作用——在定语从句中替代从句所修饰的先行词。The man who lives nest door is a famous teacher.
住在隔壁的那个人是个名师。（who 替代the man）
3. 成分作用——在定语从句中作主语、宾语、定语或状语。I like picrures which are painted in the traditional Chinese style.
我喜欢传统的中国画。（which在定语从句中作主语）
4. 当先行词为人与事物或动物时。The driver and his car that fell into the river have not yet been discovered. 掉入河里的司机与车都还没有找到。The boy and his dog that were believed to be lost in the wood were rescued this morning.
被认为在森林里迷路的孩子与狗，今天早上已经获救了。
5. 先行词在定语从句中做表语时。She is no longer the sweet girl (that) she used to be. 她再也不是过去那个甜美的女孩了。He is not the man (that) he seems. 他这人不貌相。
D．关系副词与关系代词的选择
当先行词是表示时间、地点或原因的名词时，定语从句用关系副词还是关系代词来引导，要根据关系词在定语从句中所担当的句子成分来决定。I will never forget the days when we spent our holidays together. 我永远忘不了我们一起度假的日子。（when作状语）I will never forget the days which we spent together. 我永远忘不了我们一起度过的日子。（whic作we spent宾语）I know a place where we can have a picnic. 我知道一个我们可以野炊的地方。（where作状语）I know a place which is famous for its beautiful natural scenery. 我知道一个以自然景色优美而闻名的地方。（which作主语）
E．关系词的省略
在下列情况下，关系代词或关系副词在非正式文体中可以省略。1．关系代词that, which, who, whom在定语从句中做宾语时，常可省略。Are these keys (that which) you were looking for 这是你正在寻找的钥匙吗？The man (whothat) I was sitting net to on the plane talked all the time. 飞机上坐在我旁边的那个人一直在喋喋不休。
2．以the way为先行词的限制性定语从句通常由in which或that引导，而且通常可以省略。I don like the way (that in which) she walks. 我不喜欢她走路的样子。The way (that in which) he answered the questions was surprising. 他回答这些问题的方式令惊奇。
3．在the time when, the place where, the reason why结构中，when, where, why可省略。I shall never forget the day (when) we first met. 我永远不能忘记我们第一次见面的那一天。Thats the place (where) he stayed when he was in the country. 那就是他在乡下呆过的地方。
F．定语从句与强调句型的区别
1．强调句型中的it是个引导词，本身没有意义。如果去掉it iswas�that，句子结构仍然完整，句意也完整。定语从句中的it是指示代词，做主句的主语。如果去掉it iswas�that，句子结构不完整，意思也完整。It is a question that needs careful consideration.这是一个需要慎重考虑的问题。（定语从句）It is novels that she enjoys reading.（强调句型）她喜欢阅读的是小说。（=She enjoys reading novels）
2．在强调句中被强调的部分还可以是副词、介词短语或从句；在定语从句中先行词一般是名词、代词或名词短语。It was because she was ill that we decided t return. （强调句型）正是因为她生病了，我们才决定回来。Was it in this palace that the last emperor died （强调句型）那位末朝皇帝是在这个宫殿里死的吗？Was it this palace where the last emperor died （定语从句）这是那位末朝皇帝死的宫殿吗？
3．有些强调句型中含有一个定语从句，这往往给理解带来一定的难度。解决方法是仔细分析that或who在句中的作用。It was in the labthat was set up last year that they finished the experiment.他们是在去年建造的实验室里完成这个实验的。（that was set up last year 是定语从句，that在从句中作主语，并可被which替换）It was the students who came from our school that won the first prize in the contest. 是来自我们学校的学生获得了竞赛一等奖。（who came rom our school 是定语从句，who在从句中作主语）
G．定语从句与同位语从句的区别
1．定语从句是形容词性的，其功能是修饰先行词，起限定作用。而同位语从句等同于它所修饰的名词，是名词性的，其功能是对所修饰的名词作补充说明。It is a fact (that) you can deny.这是一个你不能否认的事实。（定语从句）It is a fact that she has done her best.她尽了最大的努力，这是事实。（同位语从句）
2．在定语从句中，that代先行词，在从句中不仅起连接作用，还充当某个句子成分，在作宾语时通常可省略。而在同位语从句中，that只起连接主句和从句的作用，无意义，在从句中不充当句子成分，一般不可省。The news (that) we heard spread all over the school campus.我们听到的消息传遍了校园。（定语从句）The news that Mr. Li will be our new English teacher is true.李先生将是我们的新英语老师这个消息是真的。（同位从句）
