Form of subject-questions

subject-questions with 'Who?' Who's ready?	subject-answer + auxiliary I am/John is etc.	be
Who's got my keys?	I have /John has etc.	have
Who makes the decisions?	I do/John does etc.	do/does
Who paid the waiter?	I did /John did etc	did
Who can explain this?	I can/John can etc.	modals

subject-questions with 'What?', 'Which?' and 'Whose?'

What made you jump? The cat did

Which one suits me best? The red one does

Whose telephone rang⁷ Mine did

13 Questions, answers, negatives

Notes on the form of subject-questions

1 A subject-question normally asks for the identity of the subject.
There is no inversion and the question has the same word order as
the statement [compare > 13.31ns1,2]:

Subject verb object subject-answer

statement: Someone paid the waiter

subject-question. Who paid the waiter? John did

Compare a Who question which asks for the object of a statement:

Subject verb object object-answer

statement John paid the waiter

Yes/No question Did John pay the waiter?

Who(m)>question. Who(m) did John pay'' The waiter

2 Answers to subject-questions often echo the auxiliary used in the
question, either in the affirmative or the negative:
Who can play the piano? ~ I can /I can't

When the subject question-word is followed by a verb in the simple present or past, then do, does or did may be used in the answer: Who wants a lift? / do Who won? - We did When the answer is a name or a noun, we often omit the auxiliary: Who was at the door? - The postman (was) Informally, me is often used in place of / in the answer [> 4.7.2]: Who wants some more tea? - Me (in place of / do)

3 What, Which and Whose can combine with other subject-words: What number is? Which boy likes? Whose car is?

4 Subject question-words can be followed by singular or plural verbs. In everyday speech we commonly use a singular verb after, e.g. Who? even when we are asking for a plural answer:

Who is coming tonight? John is /John and Sally are

However, plural verbs can occur quite naturally after subject

questions with Who, Which and What:

Who are playing in the orchestra?

Who have won Nobel Prizes for literature in the past ten years?