When should I use ‘that’, ‘which’, or ‘who?
THAT can be used to refer to an object or to a group of people, but should not be used to refer to one person, for example: ‘That is a really great book’ and ‘I like to talk with that group of writers’.
WHICH should only be used to refer to objects or places, for example: ‘Which shiraz should I open?’ and ‘I don’t mind which town we visit today’.
WHO is exclusive to referring to people, for example: ‘Who is Fergal?’ and ‘Fern is the one who ate the chocolate’.
WHICH book should I read? Do you know WHO wrote THAT other book I enjoyed?