2、(用做关系代词)那一个,那一些
He also had a gun with which to defend himself.
他还有一把自卫用的枪。
3、（用作疑问形容词)哪一个,哪一些
Which university did you go to, Oxford or Cambridge?
你上过哪所大学?牛津还是剑桥?
4、(用作关系形容词)这个,这些
The doctor told him to give up smoking, which advice he took.
医生叮嘱他戒烟,他接受了这一忠告。