问题错了吧,应该是定语从句.
定语从句（Attributive Clauses）在句中做定语,修饰一个名词或代词,被修饰的名词,词组或代词即先行词.定语从句通常出现在先行词之后,由关系词（关系代词或关系副词）引出.
关系代词有：who,whom,whose,that,which等.
关系副词有：when,where,why等.
18.1 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?
他就是你想见的人吗?（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在句中作宾语）
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）
〔定语从句〕介词+关系词
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.例如：
This is the house in which I lived two years ago.这是我两年前住过的房子.
This is the house where I lived two years ago.
Do you remember the day on which you joined our club?还记得你加入我们俱乐部的那一天吗?
Do you remember the day when you joined our club?
that的比用..先行词是最高级