分别举个例子：
宾语从句：
i don't know what to do.i don't know which one is the best.象这种有what\which\that引导句子在整个句子充当宾语成分.那就是宾语从句.主语：i 谓语：don't know 宾语：what to do.
定语从句：
i don't know the man who is wearing a pair of glass.象这中由who,which,that,when 引导的句子在整个句子中做定语成分就叫定语从句.
主语：i
谓语：don't know
宾语：the man
定语：who is wearing a pair of glass.修饰the man.
状语从句：
i don't know she is my english teacher when i see her at first time.我第一眼见到她的时候,不知道她是我的英语老师.
象这样以when引导的句子在整个句子中充当状语成分的就是状语从句.
主语：i
谓语：don;t know
宾语：she is my english teacher.
状语：when 引导的句子.
