2)关系代词的省略

　　在从句中作宾语的关系代词常可省略。关系代词紧跟介词，作介词宾语时不可用that，只可用which或whom引导从句，并且不可省略，但当介词位于宾语从句句末时，作为介词宾语的关系代词仍可用that，也可省略。如：

　　This is one of those things with which we have to put up.

　　This is one of those things (whichthat) we have to put up with.

　　3)引导定语从句的关系副词有when,where,why等。关系副词在从句中作状语，意义上相当于一个“介词+which”的结构。如：

　　Even in comic books where(=in which) there are no words,the stories are fully expressed through the drawings.

　　No one knows the reason why(=for which) he was so angry that day.

　　*→非限制性定语从句

　　非限制性定语从句既可修饰先行词，也可修饰整个主句，起补充说明作用，与主句之间有逗号隔开，若省去，原句意思不受影响。不可用that引导非限制性定语从句。关系词不可省略。如：

　　Every object has a gravitational pull,which is rather like magnetism.

　　*“介词+whichwhomwhose”引导的定语从句

　　“介词+whichwhomwhose”可引导限制性定语从句，也可引导非限制性定语从句，该结构中介词的选择取决于从句谓语动词的固定搭配，或先行词的习惯搭配。如：

　　This is the computer on which he spent all his savings.

　　It is written by a person with whom we are all familiar.

　　*as引导的定语从句

　　as引导的定语从句主要用于“such...as”及“the same...as”的结构中，代替先行词是人或物的名词。as引导非限制性定语从句时，代替整个主句，从句可位于主句之前、之后或中间。如：

　　These are not such problems as can be easily solved.(as代替先行词problems)

　　As is mentioned above,no single company or group can control what happens on the Internet.(as代替主语)

　　关系副词引导的定语从句

　　关系副词可代替的先行词是时间、地点或理由的名词，在从句中作状语。

　　1)when, where, why

　　关系副词when, where, why的含义相当于"介词+ which"结构，因此常常和"介词+ which"结构交替使用，例如：

　　There are occasions when (on which) one must yield. 任何人都有不得不屈服的时候。

　　Beijing is the place where (in which) I was born. 北京是我的出生地。

　　Is this the reason why (for which) he refused our offer? 这就是他拒绝我们帮助他的理由吗?

　　2)that代替关系副词

　　that可以用于表示时间、地点、方式、理由的名词后取代when, where, why和"介词+ which"引导的定语从句，在口语中that常被省略，例如：

　　His father died the year (that / when / in which) he was born. 他父亲在他出生那年逝世了。

　　He is unlikely to find the place (that / where / in which) he lived forty years ago. 他不大可能找到他四十年前居住过的地方。

　　关系代词引导的定语从句

　　关系代词所代替的先行词是人或物的名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。

　　1)who, whom, that

　　这些词代替的先行词是人的名词或代词，在从句中所起作用如下：

　　Is he the man who/that wants to see you?

　　他就是想见你的人吗?(who/that在从句中作主语)

　　He is the man whom/ that I saw yesterday.

　　他就是我昨天见的那个人。(whom/that在从句中作宾语)

　　2) Whose 用来指人或物，(只用作定语, 若指物，它还可以同of which互换), 例如：

　　They rushed over to help the man whose car had broken down.  那人车坏了，大家都跑过去帮忙。

　　Please pass me the book whose (of which) cover is green. 请递给我那本绿皮的书。

　　3)which, that

　　它们所代替的先行词是事物的名词或代词，在从句中可作主语、宾语等，例如：

　　A prosperity which / that had never been seen before appears in the countryside. 农村出现了前所未有的繁荣。(which / that在句中作主语)

　　The package (which / that) you are carrying is about to come unwrapped. 你拿的包快散了。(which / that在句中作宾语)