1. Who came this morning?
2. Which do you prefer?
3. What does the man want?
An interrogative pronoun is one used to ask a question.
The interrogative pronouns are who, which, and what.
Who is declined as folloios:
Singular and Plural
Who refers only to persons and to things personified. Who usually asks for a person's name; as, Who is that man? But, if the name is known, it often asks for some description; as, Who is Mr. Smith?
Which may stand for either persons or things; but it differs in meaning from who and what.
When I ask, "Who did this'work?" or, "What do you want?" I am presumed to know nothing of the person or thing about whom the inquiry is made. But if I ask, "Which did this work?" or "Which do you want?" I am supposed to know more than one person or thing of the class mentioned.
What is that to you?
What could he do without your help?
What is used in either the nominative or the objective case.
The sentences, What is the man's name? What did he say? What have you done to-day? show us that the meaning of what may be singular or plural.
What has no possessive form or use. The meaning of what depends upon the idea in the mind of the questioner.