【四】定语从句：修饰前面某一名词或代词的从句叫定语从句。
由于在句中的作用相当于形容词，故也称为
形容词性从句。
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。限制性定语从句对被修饰词起到限制、修饰的作用，一般不可缺少。
非限制性定语从句起补充、附带说明作用，缺少也不会影响全句的理解。
一.限制性定语从句：限制性定语从句对被修饰词起到限制、修饰的作用，一般不可缺少。
1.由关系代词引导定语从句：关系代词：who, whom, whose, that, which, as等（在句中作主、表、宾、定等成分）
1. 关系代词在从句中作主语时，不能省略。
e.g. The classroom that is on the fourth floor is poorly equipped.
2. 关系代词在从句中作宾语且前面没有介词时，常可省略。
e.g. This is the girl with whom he works.
In this earthquake, the number of people who lost homes reached as many as 250,000.
I have many good friends to whom I am going to send postcards.
You’re the only person whose advice he might listen to.
The river which runs through the center of the city brings us a lot of pleasure.
He has given us as much advice as he can.
【例】The man to whom you talk just now is a famous runner.
【例】The service about which the students complain a lot should be improved.
【例】He is a library assistant from whom I borrowed some books.
【例】It is a famous school from which he graduated 3 years ago.
【例】The chair on which he is sitting now is made of wood.
The man (who/that/whom) you talk to just now is a famous runner.
【例】The service (which/that) the students complain about a lot should be improved.
He is a library assistant (whom/that/who) I borrowed some books from.
【例】It is a famous school (which/that) he graduated from 3 years ago.
【例】The chair (which/that) he is sitting on now is made of wood.
有一些动词短语中的介词是固定搭配，不可以拆开，一般还是放在动语之后，不提前：
【例】He is the student (who/whom/that) the teachers are looking for.
【例】The number of the children (who/whom/that) she takes care of is 3
【五】同位语从句
同位语从句与定语从句的区别（一）
同位语从句与定语从句形相似而实质不同，具体表现在以下几个方面：
1. 被修饰的词不同：同位语从句的前面一般是数量有限的、表示抽象意义的名词；而定语从句的
先行词是无数的指人或物名词。
2. 从句的作用不同：同位语从句表示同位名词的具体内容，而定语从句是对先行词的限制、描绘或说明。
3. 引导词不同：what, how, whether等不能用引导定语从句，但可用于引导同位从句。
4. 引导词的作用不同：引导同位语从句的that是连词，在从句中不充当任何成分；而引导定语从句的that为关系代词，在从句中充当一定的
句子成分。
5. 判定定语从句和同位语从句的方法：由于同位语从句是用以说明被修饰名词的具体内容的，所它可以转换同位名词的
表语；而定语从句则不能作这种转换。
同位语从句与定语从句的区别（二）
一、从句法功能上来看
同位语从句中连接词that在从句中不作句子成分，也没有词汇含义，只起连接作用，其作用大致相当于一个冒号；而引导定语从句的that是关系代词，且在句中充当句子的成分(主语或宾语)。如：
I hold the belief that where there is a will, there is a way. (that引导的是同位语从句，它在从句中不充当句子成分)
The letter that I received yesterday was from my sister. (that引导的是定语从句，它在从句中充当宾语)
二、从意义上来看
同位语从句所表达的内容与作为
中心词的名词所表达的内容是一样的，两者之间可以划等号；而定语从句则是限制或修饰中心词的，中心词所表达的内容不等于定语从句所表达的内容。如：
He told me the news that his uncle would come home from abroad on
National Day. (that引导的是同位语从句，其中the news = his uncle would come home from abroad on National Day)
This is the factory that we visited last month. (that引导的是定语从句，其中 the factory≠ we visited last month.)
三、从中心名词上来看
同位语从句中的中心名词常是一些表示概括意义的抽象名词，这类名词有fact, idea, view, thought, order, suggestion, news, truth, hope, promise, answer, belief, condition, doubt, fear, problem, proof, question 等。而定语从句中的中心名词是没有限定的。如：
四、从that是否可以省略来看
引导同位语从句的连词that一般不能省略，而在定语从句中，that作宾语时，可以省略。另外，引导定语从句的that若指事物，它可以用which来代替，而在同位语从句中，that 永远不能用which替代。
同位语从句的引导词问题
■最常用的引导词
用以引导同位语从句的最常用的连词是that。如：
The news that we are having a holiday tomorrow is not true. 明天放假的消息不实。
The idea that you can do this work without thinking is wrong. 你可以不动脑筋做此工作的想法是错误的。
有时也可以用whether、连接代词或连接副词等来引导。如：
It is a question how he did it. 那是一个他如何做的问题。
Do you have any idea where he lives? 你知道他住在哪里吗?
She had no idea why she thought of him suddenly. 她不明白她为什么突然想到了他。
We are not investigating the question whether he is trustworthy. 我们不是在调查他是否可信赖的问题。
■ 同位语从句可以用if引导吗
表示“是否”的whether可以引导同位语从句，但是与之同义的if不能用于引导同位语从句。如：
他是否会来还不一定。
误：There is some doubt if he will come.
正：There is some doubt whether he will come.
让我们来讨论是否该做的问题吧。
正：Let’s discuss the question if we should do it.
正：Let’s discuss the question whether we should do it.
■ 同位语从句可以用which引导吗
大家知道，在定语从句中，若先行词为指事物的名词，有时既可用that来引导定语从句，也可用which来引导定语从句，但在同位语从句中，习惯上要用that，而不用which。如：
我坚信他会获胜。
误：I hold a firm belief which he will win.
正：I hold a firm belief that he will win.
我得出结论这样做是不明智的。
误：I've come to the conclusion which it was unwise to do that.
正：I've come to the conclusion that it was unwise to do that.
■ 同位语从句可以用what引导吗
what不能用于引导定语从句，但可以引导同位语从句，尤其用于idea之后。如：
Have you any idea what time it starts? 你知道什么时候开始吗?
I didn’t have the faintest idea what you meant. 我一点也不明白你是什么意思。
Do you have any idea what it means to be poor? 你知道贫穷意味着什么吗?
一、强调句
为了突出某一部分重要信息，常常借用语法中的变换句子的正常语序，将某个成分置于句首或句末，或者通过词汇手段突出句子的某个成分。
1. it 为先行词的强调结构
It was Li Ping who told me the news. (强调人时才能用who)
It was in the park that I met him. (强调地点不能用where，只能用that)
It was yesterday that I saw him off at the airport. (强调时间不能用when，只能用that)
2.
助动词do 的强调作用
在行为动词作谓语的句子中，常用“助动词do或did” + 谓语“动词原形”表示强调语气。
例如：She did go to see him yesterday.
We do have four lessons in the morning.