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.
区别于 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.