用who、whom、which链接下面句子

问题描述:

用who、whom、which链接下面句子
He is the policeman.He caught the thieves.
She is the woman.I met her yesterday.
I am a person.I wrote to you.
These are things.I bought the yesterday.

He is the policeman who caught the thieves.She is the woman whom I met yesterday.I am the person who wrote to you.These are the things which I bought the yesterday.