Charles Smith， who was my former teacher， retired last year. 查理·史密斯去年退休了，他曾经是我的老师。

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

　　This novel， which I have read three times， is very touching. 这本小说很动人，我已经读了三遍。

　　3) 非限制性定语从句还能将整个主句作为先行词， 对其进行修饰， 这时从句谓语动词要用第三人称单数，例如：

　　He seems not to have grasped what I meant， which greatly upsets me. 他似乎没抓住我的意思，这使我心烦。

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

　　说明：关系代词that和关系副词why不能引导非限制性定语从句。

　　1)介词后面的关系词不能省略。

　　2)that前不能有介词。

　　3) 某些在从句中充当时间，地点或原因状语的"介词+关系词"结构可以同关系副词when 和where 互换。

　　This is the house in which I lived two years ago.

　　This is the house where I lived two years ago.

　　Do you remember the day on which you joined our club?

　　Do you remember the day when you joined our club?

　　由as， which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。As一般放在句首，which在句中。

　　As we know， smoking is harmful to one's health.

　　The sun heats the earth， which is very important to us.

　　典型例题

　　1)Alice received an invitation from her boss， ___came as a surprise.

　　A. it B. that C. which D. he

　　答案C. 此为非限定性从句，不能用 that修饰，而用which.，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。

　　2)The weather turned out to be very good， ___ was more than we could expect.

　　A. what B. which C. that D. it

　　答案B。which可代替句子，用于非限定性定语从句，而what不可。That 不能用于非限定性定语从句，it不为连词，使由逗号连接的两个句子并在一起在英语语法上行不通。

　　3)It rained hard yesterday， ____ prevented me from going to the park..

　　A. that B. which C. as D. it

　　答案B.

　　as 和which在引导非限制性定语从句时，这两个关系代词都指主句所表达的整个意思，且在定语从句中都可以作主语和宾语。但不同之处主要有两点：

　　(1) as 引导的定语从句可置于句首，而which不可。

　　(2) as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词;若为行为动词，则从句中的关系代词只能用which.。

　　在本题中，prevent由于是行为动词，所以正确选项应为B。

　　As 的用法

　　例1. the same… as;such…as 中的as 是一种固定结构， 和……一样……。

　　I have got into the same trouble as he (has).

　　例2. as可引导非限制性从句，常带有'正如'。

　　As we know， smoking is harmful to one's health.

　　As is know， smoking is harmful to one's health.

　　As是关系代词。例1中的as作know的宾语;例2中，它充当从句的主语，谓语动词know要用被动式。

　　1)Whoever spits in public will be punished here.

　　(Whoever 可以用 anyone who 代替)

　　2)The parents will use what they have to send their son to technical school.

　　(what 可以用all that代替)

　　1)what = the thing which;whatever = anything

　　What you want has been sent here.

　　Whatever you want makes no difference to me.

　　2) who= the person that whoever= anyone who

　　(错)Who breaks the law will be punished.

　　(错)Whoever robbed the bank is not clear.

　　(对)Whoever breaks the law will be punished.

　　(对)Who robbed the bank is not clear.

　　3) that 和 what

　　当that引导定语从句时 ，通常用作关系代词，而引导名词性从句时，是个不充当任何成分的连接词。宾语从句和表语从句中的that常可省略。What只能引导名词性从 句， 用作连接代词，作从句的具体成分，且不能省略。

　　I think (that) you will like the stamps.

　　What we need is more practice.

　　1)不用that的情况

　　a) 在引导非限定性定语从句时。

　　(错) The tree， that is four hundred years old， is very famous here.

　　b) 介词后不能用。

　　We depend on the land from which we get our food.

　　We depend on the land that/which we get our food from.

　　2) 只能用that作为定语从句的关系代词的情况

　　a) 在there be 句型中，只用that，不用which。

　　b) 在不定代词，如：anything， nothing， the one， all， much， few， any， little等作先行词时，只用that，不用which。

　　c) 先行词有the only， the very修饰时，只用that。

　　d) 先行词为序数词、数词、形容词最高级时，只用that。.

　　e) 先行词既有人，又有物时。

　　举例：

　　All that is needed is a supply of oil.

　　所需的只是供油问题。

　　Finally， the thief handed everything that he had stolen to the police.