定语从句就是用在中心词后面起修饰作用的从句,相当于形容词.像people who is stronge中who is stronge就是从句修饰people．
主语从句.宾语从句是用做主语.宾语的句子．
what引导主语从句.宾语从句,在句中充当主语.宾语
that which引导定语从句中,