定语从句，又称为关系从句，顾名思义在句中有着修饰限定的作用，可修饰单一的词，也可修饰一个句子。其中被定语从句修饰的词称为先行词，定语从句由关系词引导，被定语从句修饰的词叫作先行词。
关系代词：who, which, who, whom, whose
关系副词：when, where, why, how
关系词的作用：除引导从句外，还代替先行词在从句中充当一定的成分，如主语，宾语，定语，状语等。
1. 关系代词引导的定语从句
1.1 关系代词的作用：
关系代词可以代替指人和物的先行词，在从句起主语，宾语，定语的作用。
A. Where was the man who had made a great progress in studying archaeology.
在研究考古学方面取得伟大成就的人在哪？
B.The woman whom you met is our teacher.
你刚才看到的那个女士是我们的老师。
C.She had brought these flowers which died at last year.
她买的这些花儿在去年都凋谢了。
D.Is there someone whose booklet have lost in library.
有谁的手册落在图书馆了吗？
A.The city where a new building is going to be built.
这座城市将有一个新的建筑被修建。
B.He wants to know the reason whyhe failed in the game.
他想知道为什么他会在比赛中失败的原因。
C.We arrived there at eveningthe store closed.
我们在店铺打烊的晚上到了。
A.He own a house which has a swimming pool, actually.
事实上，他拥有一个有着游泳池的房子。
B.He own a house,which has a swimming pool, actually.
事实上，他拥有一个房子，这个房子带有游泳池。
A.He is from China,as I know from his accent.
正如我从他的口音得知，他来自中国。
