det, pron

 

choice used to ask or talk about a choice between two or more things

Which of these do you like best?

 

referring to something used at the beginning of a relative clause to show what thing is being referred to

These are principles which we all believe in.

 

extra information used to give more information about something

The book, which includes a map, gives you all the information you need about Venice.

 

giving opinion used when you give an opinion about what you have just said

He took us both out for lunch, which I thought was very kind of him.