1. 关系代词有：that,which,who,whom,whose,在定语从句中作主语、宾语中表语，whose作定语。代人的有：who,whom,whose,that;代物的有：that,which,whose.例如：
The man who helped you is Mr White.(who代人，在定语从句中作主语)
That is the person(whom/who/that) you want to see.(whom,who,that代人，在定语从句中作宾语，可省略)
Im not the fool(that) you thought me to be.(that代人，在定从中作表语)
A dictionary is a useful book which(=that) tells us the meaning of words(which或that代物，在定从中作主语)
2. 关系副词有：when(指时间)，where(指地点),why(指原因)，在定语从句中作状语。
例如：Would you suggest a time(when) we can have a talk?(when可省略)
The house where they live is not very large./This is the reason why he did not came to the meeting.
注意：不是表时间的先行词都用when引导定从，不是表地点的先行词都用where引导定从。例如：Well visit the factory which(=that) makes radios.
(which或that在定从中作主语，where不可用主语，故不可用)
They still remember the happy days(which/that) they spent in Beidaihe.
(which或that在定从中作spent的宾语，when不可作宾语，故不可用)
定语从句引导词及用法
引导定语从句的关联词称为关系词，关系词有关系代词和关系副词。关系代词有that, which, who, whom, whose, as等；关系副词有where, when, why等。关系词常有3个作用：
1、引导定语从句。
2、代替先行词。
3、在定语从句中担当一个成分。
关系副词引导的定语从句
1. when指时间，在定语从句中做时间状语
(1) I still remember the day when I first came to the school.
(2) The time when we got together finally came.
2. where指地点，在定语从句中做地点状语
(1) Shanghai is the city where I was born.
(2) The house where I lived ten years ago has been pulled down.
3. why指原因，在定语从句中做原因状语
(1) Please tell me the reason why you missed the plane.
(2) I don’t know the reason why he looks unhappy today.
注意：关系副词引导的从句可以由“介词+关系代词”引导的从句替换
(1) The reason why/ for which he refused the invitation is not clear,
(2) From the year when/in which he was going to school he began to know what he wanted when he grew up.
(3) Great changes have taken place in the city in which./where I was born.
