who 在陈述句中就已经不是疑问词了，而是变成了引导词，引导各种从句。
Who you are is very important to us. 主语从句
I don't care who you are. 宾语从句
The important thing is who you are talking to just now. 表语从句
A teacher is a person who teaches knowledge to us. 定语从句
在主谓宾结构，who开头的陈述句做宾语，而who 是陈述句的主语。如：Nobody knows who eats the apple.
