Wh-questions with how, which, what and who

Study these sentences:
• Which biscuits did you make - the chocolate ones or the others? (rather than What...?)
• I've got orange juice or apple juice. Which would you prefer? (rather than What...?)
• He just turned away when I asked him. What do you think he meant? (not Which...?)
• What do you want to do this weekend? (not Which...?)
We usually use which when we are asking about a fixed or limited number of things or people, and what when we are not. Often, however, we can use either which or what with little difference in meaning. Compare:
• What towns do we go through on the way? (the speaker doesn't know the area) and
• Which towns do we go through on the way? (the speaker knows the area and the towns in it)
We usually use who to ask a question about people:
• Who will captain the team if Nick isn't available?
However, we use which when we want to identify a person or people out of a group (for example, in a crowded room, or on a photograph) and when we ask about particular classes of people. We can use what to ask about a person's job or position:
• 'Which is your brother?' 'The one next to Ken.'
• Which would you rather be - a doctor or a vet? (or What would...?)
• 'What's your sister?' 'She's a computer programmer.'
We use which, not who or what, in questions before one(s) and of:
• Which one of us should tell Jean the news? (ио£ Who one of us...?)
• I've decided to buy one of these sweaters. Which one do you think I should choose? (rather than What one do you think...?)
• Which of these drawings was done by you? (not What of...)
• Which of you would like to go first? (not Who of...)
When we use who or what as a subject, the verb that follows is singular, even if a plural answer is expected:
• Who wants a cup of coffee? (said to a number of people)
• What is there to do in Leeds over Christmas? (expects an answer giving a number of activities)
Study the use of how and what in these questions:
• What's this one called? (not How...)
• What do you think of her work? (not How...)
• What is the blue button for? (= What purpose does it have?) (not How...)
• How about (having) a swim? (= a suggestion) (or What about...)
• What is your brother like? (= asking what kind of person he is) (not How...
• How is your brother? (= asking about health) («of What...
• What was the journey like? (= asking an opinion) (not How.
• How was the journey? (= asking an opinion) (not What...
•What do you like about it? (= asking for specific details) (not How...)
• How do you like it? (not What...) = asking for a general opinion = asking for details about coffee, tea or a meat dish ('How would you like it?' is also possible)