I. Determiners

1. We can use which and what before nouns to ask questions about people or things

• Which teacher do you like best?
• Which colour do you want – green, red, yellow or brown?
• What writers do you like?
• What colour are your girl-friend’s eyes

1. We usually prefer which when we are choosing between a small number, and what when we are choosing between  a large number.
2. Before another determiner (for example the, my, these) or a pronoun, we use which of

• Which of your teacher do you like best?
• Which of them do you want

II. Pronouns

1. We can use which, what and who as pronous, without nouns. We use who, not which for people

• Who won- Smith or Fitzgibbon
• Which would you prefer – wine or beer?
• What would you like to eat?

1. We usually use who , not whom , as an object

• Who do you like best – your father or your mother?
• Whom do you like best…? (is very formal)