which
Which can be a determiner or a pronoun.
asking for information
You use which when you are asking for information about one of a limited number of things or people. A noun phrase beginning with which or consisting of the pronoun which can be the subject, object, or complement of a verb. It can also be the object of a preposition.
Which type of oil is best?
Which is her room?
Be careful
When the noun phrase is the object of a verb or preposition, you put an auxiliary verb after the object, followed by the subject and the main verb. When the noun phrase is the object of a preposition, the preposition usually goes at the end of the clause.
When the noun phrase is the object of a verb or preposition, you put an auxiliary verb after the object, followed by the subject and the main verb. When the noun phrase is the object of a preposition, the preposition usually goes at the end of the clause.
Which hotel did you want?
Which station did you come from?
used in reported clauses
Which is often used in reported clauses.
Do you remember which country he played for?
I don't know which to believe.
used in relative clauses
Which can be a relative pronoun in both defining and non-defining relative clauses. In relative clauses, which always refers to things, never to people.
We heard about the awful conditions which exist in some prisons.
I'm teaching at the local college, which is just over the road.
In relative clauses, you can use either which or who after a collective noun such as family, committee, or group. After which you use a singular verb. After who you usually use a plural verb.
He is on the committee which makes decisions about planning.
They are a separate ethnic group who have their own language.
Be careful
When which is the subject of a non-defining clause, don't use another pronoun after it. Don't say, for example, ‘He stared at the painting, which it was completely ruined’. You say ‘He stared at the painting, which was completely ruined’.
When which is the subject of a non-defining clause, don't use another pronoun after it. Don't say, for example, ‘He stared at the painting, which it was completely ruined’. You say ‘He stared at the painting, which was completely ruined’.