1. who, whose, whom - 사람을 대신한다.
This is the girl. She is a good secretary. –> This is the girl who is a good secretary.
I employed a man. I thought (that) he was honest. –> I employed a man who I thought was honest.
This is the boy. I wanted to see him. –> This is the boy whom I wanted to see.
I employed a man. I thought him to be honest. I employed a man whom I thought to be honest.
A child is called an orphan. His parents are dead. –> A child whose parents are dead is called an orphan.
2. which - 사람이나 구절을 대신한다.
I have a book. It is very interesting. –> I have a book which is very interesting.
This is the dictionary. I bought it yesterday. –> This is the dictionary which I bought yesterday.
This is the word. I don't know the meaning of it. –> This is the word which I don't know the meaning of. –> This is the word of which I don't know the meaning. –> This is the word the meaning of which I don't know. –> This is the word of which the meaning I don't know. –> This is the word whose meaning I don't know.
They tried to persuade her, which turned out to be useless. I said nothing, which made her angry.
3. that - 사람이나 사물을 대신한다.
3.1. 선행사가 the only, the very, the same과 같은 말을 수식하는 경우.
This is the last money that you shall ever receive from me.
3.2. 선행사가 all, no, little, much, -thing, -one, -body 단어일 경우.
No man that knows the fact will think me guilty. There was little that interested him at the show window. I'll give you everything that I have.
3.3. 선행사가 사람 + 사물인 경우
A man and his dog that were passing by were injured.