定语从句：
The boys who are playing football are from Class One.
Yesterday I helped an old man who lost his way.
Mr. Liu is the person (whom) you talked about on the bus.
Football is a game which is liked by most boys.
Where is the man (that/whom) I saw this morning?
宾语从句：
I don't know what he is looking for.
She said that she would leave the message on the headmaster's desk.
I wonder whether we stay or whether we go.
Let me know whether / if he will come or not.(= Let me know whether or not he will come ).
Could you tell me where we will have the meeting this afternoon?