语法填空中while的用法什么时候用while什么时候用when?有什么区别?

语法填空中while的用法
什么时候用while什么时候用when?有什么区别?

如果你会合并下列句子,你的这个问题就OK了：
He came She was wating
1 When he came,she was waiting
2 While she was waiting,he came
3 She was waiting when he came
4 He came while she was waiting