1、先看一个例子，
I don’t like lazy people.
I don’t like people who never keep their word.
第一句，lazy修饰people，说人懒，所以lazy是定语。
第二句， who never keep their word修饰people, 是一句话修饰people，
所以是定语从句。
people，是被定语从句修饰的词，称为先行词。
who是连接两个句子，并且指代people, 称为连接代词
2、类似的，连接代词主要有who, which, that, whom, whose, 起代词和连接句子两个作用，从句中充当主语或宾语（whose做定语, 表示隶属，谁的）
看下边的例子，
a. People who have pets are usually kind and warm.
b. I don’t like stories which have unhappy endings.
c. Not everything that is learned is contained in books.
d. People need friends with whom they can share secrets.
e. There are some children whose parents are too busy to take care of them.
可以用上面介绍的方法来理解这些句子。
