在复合句中修饰名词或代词的从句叫定语从句。根据定语从句与先行词的关系是否紧密，可分为限制性定语从句和非限制性定语从句。

　　限制性定语从句和非限制性定语从句的区别如下：

　　具体说来有四点不同：

　　限制性定语从句紧跟在先行词后面，不能用逗号把从句与先行词分隔开来；非限制性定语从句通常由逗号与句子其他成分隔开。如：

　　This is the New Bora which I bought last month. 这是我上个月买的那辆新宝来轿车。（限制性）

　　The New Bora， which I bought last month， is very nice. 这辆新宝来轿车很漂亮，是我上个月买的。（非限制性）

　　This summer I went to Shanghai Expo， where I spent 5 days and saw a lot of attractive things. 今年夏天，我去了上海世博会，在那儿待了五天，观览了很多魅力无穷的事物。（非限制性）

　　The expression “Oh， my Lady Gaga”， which is used to express one?蒺s surprise， is very popular among children these days. 用来表达惊讶的话语“Oh， my Lady Gaga”如今在孩子们中间很盛行。（非限制性）

　　限制性定语从句与先行词的关系非常密切，是先行词不可缺少的定语，它所修饰的词代表一个（些）或一类特定的人或物，如果删去，全句的意思就会变得不明确；而非限制性定语从句在意义上是先行词的一个附加修饰语，对先行词只起进一步补充说明的作用，若把它去掉，句子仍能成立，全句意思仍然清楚。请比较下面两组句子：

　　My son who is 18 years old is a college student.

　　我18岁的那个儿子是个大学生。

　　My son， who is 18 years old， is a college student.

　　我儿子是大学生，今年18岁。

　　第一句中，限制性定语从句限制了先行词的意义，明确是18岁的那个儿子（而不是其他的，即有可能还有其他儿子）。第二句使用了非限制性定语从句，表明可能只有一个儿子，他今年18岁，起补充说明作用。再如：

　　The girl who stood in the corner just now is my younger sister. 刚才站在角落里的那个姑娘是我的妹妹。

　　Mary Smith，who is in the corner， wants to meet you. 玛丽·史密斯在那个角落里，她想见你。

　　第一个例句中的定语从句指明作为主语的“姑娘”不是任何一个，而是在角落的那个；如果去掉定语从句，表达的意思就不明确。第二个例句已经表明主语是谁，定语从句只不过是补充说明一点情况而已；若去掉从句，句子意思仍然完整。

　　限制性定语从句的先行词通常是名词或代词，而非限制性定语从句的先行词除名词或代词外，还可以是整个主句（此时，常用which或as引导从句）。如：

　　All that is needed is a supply of oil. 所需要的只是一些油而已。（限制性）

　　Pleasant Goat and Big Big Wolf is one of the best cartoons， which is loved by both children and adults. 《喜羊羊与灰太狼》是最好的卡通片之一，深受儿童和成年人的喜爱。（非限制性）

　　As has been announced， there were 42 deaths in the airplane crash in Yichun. 正如所宣布的一样，在伊春空难中有42人遇难。（句中as是关系代词，引导非限制性定语从句，指代后面整个主句的内容。）

　　在把限制性定语从句译成汉语时，通常在从句的末尾加“的”字，放在它所修饰名词的前边。而在把非限制性定语从句译成汉语时，一般译成一个单独的句子。限制性定语从句中通常先译从句后译先行词；而非限制性定语从句中则往往相反。如：

　　He is a man who/that never leaves today?蒺s work till tomorrow. 他是一个从不把今天的工作留到明天去做的人。（限制性）

　　This is my secretary Lucy，who never leaves today?蒺s work till tomorrow. 这是我的秘书露西，她从不把今天的工作留到明天去做。（非限制性）

　　We are living in an age when many things are done on computer. 我们生活在一个许多工作都由电脑来完成的时代。（限制性）

　　The 2010 Youth Olympic Games， which is hosted by Singapore is attended by 3，200 athletes between 14 and 18. 2010年青奥会有3200名14到18岁的年轻运动员参加，本届青奥会由新加坡承办。（非限制性）

　　After graduating from college， I took some time off to go travelling， which turned out to be a wise decision. 大学毕业后，我休假一段时间去旅游，结果证明是一个明智的决定。（非限制性）

　　1. 非限制性定语从句的先行词是短语或句子时，从句谓语动词要用第三人称单数。如：

　　Peter drove too fast， which was very dangerous. 彼得开车很快，这是很危险的。

　　Yao Ming， who has come back， attracted a lot of attention. 姚明复出了，这吸引了很多关注。

　　He likes playing table tennis， which benefits him greatly. 他喜欢打乒乓球，这使他受益颇多。

　　Liquid water changes to vapor， which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。

　　On Aug 7， 2010， a powerful mudslide hit Zhouqu County， Gansu Province， which led to a great loss. 2010年8月7日，甘肃舟曲县发生特大泥石流，导致巨大损失。

　　2. 当先行词为专有名词或被物主代词和指示代词所修饰时，要用非限制性定语从句修饰。如：

　　Mr. Smith， who is our boss， will leave for Japan next week. 我们的老板史密斯先生下周要去日本。

　　My house， which I bought last year， has got a lovely garden. 我去年买的那幢房子带着个漂亮的花园。

 

The movie Aftershock， which is directed by Feng Xiaogang， moves a lot of audience. 电影《唐山大地震》由冯小刚执导，感动了无数的观众。

　　3. 关系代词that和关系副词why不能引导非限制性定语从句。

　　例1 他送给他母亲一台彩电作为生日礼物，这使她非常高兴。

　　误：He gave his mother a color TV set for her birthday， that pleased her a lot.

　　正：He gave his mother a color TV set for her birthday， which pleased her a lot.

　　例2 他没通过这次考试，令我很失望。

　　误：He didn?蒺t pass the exam， that disappointed me.

　　正：He didn?蒺t pass the exam， which disappointed me.

　　as和which引导的非限制性定语从句

　　1.由as， which引导的非限制性定语从句，as和which都能指代整句内容。如：

　　As we know， smoking is harmful to one?蒺s health. 正如我们所知，吸烟有害健康。

　　A five?鄄year?鄄old boy can speak two foreign languages， which surprises all the people present. 一个五岁男孩会讲两门外语，这令所有在场的人感到非常惊讶。

　　2. as可以引导一个非限制性定语从句，常常有“正如……”的意思。这种定语从句既可置于主句之前，也可置于主句之后，而which引导的非限制性定语从句只能置于主句之后，相当于and this或and that。如：

　　As is known to all， water is an important kind of natural resource. 众所周知，水是一种重要的自然资源。

　　He died of cancer， as is expected. 正如所料，他死于癌症。

　　We moved the big stone away from the road， which took us an hour.=We moved the big stone away from the road， and that took us an hour. 我们把那块大石头从路上搬走了，这花去了我们一个小时的时间。

　　3. as引导限制性定语从句，先行词前常被such，the same，so修饰，即构成such ... as，the same ... as，so ... as结构。as在定语从句中充当的成分是主语、宾语或表语。如：

　　I have got into the same trouble as he （has）. 我陷入了和他遇到的一样的麻烦。

　　These houses are sold at such a low price as people expected. 如人们所料，这些房子以如此低的价格出售。

　　即学即练

　　1. Please show me the book___________cover is red.

　　A. who B. whom

　　C. which D. whose

　　2. As a child， Jack studied in a village school，___________is named after his grandfather.

　　A. which B. where

　　C. what D. that

　　3. The settlement is home to nearly 1?郯000 people， many of___________left their village homes for a better life in the city.

　　A. whom B. which

　　C. them D. those

　　4. Children who are not active or___________diet is high in fat will gain weight quickly.

　　A. what B. whose

　　C. which D. that

　　5. Whenever I met her，___________was fairly often， she greeted me with a sweet smile.

　　A. who B. which

　　C. when D. that

　　6. They?蒺ve won their last three matches ，

　　___________ I find a bit surprising actually.

　　A. that B. when

　　C. what D. which

　　7. My friend showed me round the town ，

　　 was very kind of him.

　　A. which B. that

　　C. where D. it

　　8. Because of the financial crisis， days are gone___________local 5?鄄star hotels charged 6，000 yuan for one night.

　　A. if B. when

　　C. which D. since

　　9. Gun control is a subject___________Ameri?鄄cans have argued for a long time.

　　A. of which B. with which

　　C. about which D. into which

　　10. —What do you think of teaching， Bob？

　　 —I find it fun and challenging. It is a job___________you are doing something serious but interesting.

　　A. where B. which

　　C. when D. that