asking for information specifying one or more people or things from a definite set

which are the best varieties of grapes for long keeping?

which of the suspects murdered him?

which way is the wind blowing?

used referring to something previously mentioned when introducing a clause giving further information

a conference in Vienna which ended on Friday

it was a crisis for which he was totally unprepared

your claim ought to succeed, in which case the damages will be substantial

asking for information specifying one or more people or things from a definite set

which are the best varieties of grapes for long keeping?

which of the suspects murdered him?

which way is the wind blowing?

used referring to something previously mentioned when introducing a clause giving further information

a conference in Vienna which ended on Friday

it was a crisis for which he was totally unprepared

your claim ought to succeed, in which case the damages will be substantial