1)when 指时间，在从句中作时间状语，它的先行词通常有time，day，morning，night，week，year 等。如：?

I still remember the time when I first became a college student.?

我仍然记得我成为大学生的那个时刻。?

Do you know the date when Lincoln was born? 你知道林肯出生的日期吗??

注：when时常可以省略，特别是在某些句型和某些时间状语中。如：?

Each time he came，he did his best to help us.每次他来，都尽他所能帮我们。?

2)where指地点，在从句中作地点状语。它的先行词通常有place，spot，street，house，room，city，town，country等。如：?

This is the hotel where they are staying.这是他们住的旅馆。?

I forget the house where the Smiths lived.我不记得史密斯先生住过的房子了。?

注：where有时也可以省略。如：?

This is the place (where)we met yesterday. 这是我们昨天见面的地方。?

3)why指原因或理由，它的先行词只有reason。如：?

That is the reason why he is leaving so soon.那就是他为什么要离开的原因。?

注：why时常也可以省略。如：?

That is the real reason he did it.那就是他做此事的真正原因。

4.使用关系副词应注意下列几点：?

1)这三个关系副词在意义上都相当于一定的介词+which结构：?

when = on (in，at，during...)+which;?

where = in (at，on...)+which;?

why = for which.如：?

I was in Beijing on the day when (=on which)he arrived.?

他到的时候，当时我正在北京。?

The office where (=in which)he works is on the third floor.?

他工作的办公室在?三楼。??

This is the chief reason why (=for which)we did it.这是我们做这件事的主要原因。?

2)当先行词是表时间的time，day等和表地点的place，house等时，一定要注意分析从句的结构，如果缺少主语或宾语时，关系词应该用which或that,缺少时间状语或地点状语时，才能用when或where，试比较：?

I’ll never forget the day when my hometown was liberated.?

我将永远不会忘记我的家乡被解放的那一天。?

I’ll never forget the days which/that we spent together last summer.?

我将永远不会忘记去年夏天我们共同度过的那段时光。?

3)when和where既可以引导限制性定语从句，也可以引导非限制性定语从句。而why 只能引导限制性定语从句。??

三、“介词+关系代词”引导的定语从句?

在这种结构中，关系代词若是表示人时，就只能用whom;关系代词若是表示事物时，就只能用which。

1.当介词放在关系代词的前面时，介词宾语只能用which (指物)或whom 关系代词不能省略。如：

He has found a good job for which he is qualified.?

他找到了一份他能胜任的工作。?

(qualify + 名词+for意为“使……具有……资格”)?

The man to whom you talked just now will chair the meeting tomorrow.?

你刚才与他谈话的那个人明天主持那个会议。( talk to+名词意为“与某人谈话”)?

He is bargaining with the landlord over the monthly price at which the apartment rents. 他在与房东就那套公寓出租的月租金进行磋商。(名词+rent at+表示价格的词意为“某物以某价格出租”)

2.当介词位于定语从句的末尾时，可用that/which(指物)，that/whom/who(指人)作介词的宾语，而且作介词宾语的关系代词往往省略。如：?

This is the hero (that/who/whom)we are proud of.这就是我们引以为豪的英雄。?

This is the pen ( that/which)I wrote the letter with.这就是我用来写信的那枝笔。

3.“复合介词短语+关系代词which”引导的定语从句，这种结构引导的定语从句常与先行词用逗号分开，定语从句常用倒装语序。?

He lived in a big house，in front of which stood a big tall tree.?

他住在一所大房子里，房前有一棵大高树。?

The monkey crossed the river，in the middle of which he was almost killed.?

那只猴子过了河，在河中央它差点淹死。?

注意：在一些固定搭配的动词短语中，由于动词和介词不可分割，因此不能把介词置于关系代词之前。如：?

This is the pen which I’m looking for.这正是我在寻找的那枝笔。?

The boys he is looking after are very healthy. 他照看的那些小男孩都很健康。

4.介词+关系代词=关系副词?

1)这就是我们去年住过的房间。?

This is the room which we lived in last year.?

This is the room in which we lived last year.?

This is the room where we lived last year.?

2)我仍然记得我入党的那一天。?

I still remember the day on which I joined the Party.?

I still remember the day when I joined the Party.?

通过对上述知识的掌握，对于一个句子我们可用不同的表达方法来表达。如：?

那就是他工作的大学。?

四、定语从句的种类以及区别

1.定语从句分为限制性定语从句和非限制性定语从句，现将它们之间的用法及区别列表如下

限制性定语从句 非限制性定语从句

和先行词的关系密切(删去后，影响整个句子意义的表达) 和先行词的关系不密切(是一种补充说明，删去后不影响整个句子意义的表达)

不用逗号分开 一般使用逗号分开

可用关系代词that引导 不可用关系代词that引导

可以省略(that，who，which在从句中担当宾语时可以省略) 不可以省略

可以替代(whom作宾语时，可用who或that替代) 不能替代

只可以修饰先行词，不可以修饰主句或主句的一部分 修饰整个主句或主句的一部分，此时定语从句前有逗号分开，只能用which或as引导。

请看下面例句的不同含义：?

限制性：她有两个当解放军的儿子。?

She has two sons who are P.L.A.men.?

(Maybe she has other sons who are not P.L.A.men.)?

非限制性：她有两个儿子，他们都是解放军。?

She has two sons，who are P.L.A.men.?

(She has only two sons.They are both P.L.A.men.)?

体会下列非限制性定语从句?

Yesterday I met Li Ping，who seemed to be busy.?

昨天我遇到了李平，他看起来?很忙。??

We will put off the meeting until next week，when we won’t be so busy.?

我们将把会议推迟到下周举行，到那时我们就不会这么忙了。

2.关系代词which与as引导定语从句的区别?

which与as都可以引导定语从句，但它们有许多用法上的区别，现就此简要分析如下：??

1)which与as引导非限定性定语从句的区别：?

which只能放在主句后面，而as引导的从句位置相对较灵活，可在前，可在后。如：?

As he realized，I was very useful to him.?

(在前)正像他所意识到的那样，我对他非常有用。?

Air，as we know，is a gas.(在中)空气，众所周知，是一种气体。?

He was a foreigner，as I know from his accent.?

(在后)他是个外国人，正像我从他的口音判断的那样。?

He came late again，which made his boss angry.?

(在后)他又来晚了，这一点使得老板很生气。?