Hi azeegum,
The interrogative pronouns are: who, whom, whose, what and which. They have nominal functions:
1)Subject:
Who opened my letter? (who: subject; opened my letter: predicate)
When the wh-element is the subject it is immediately followed by the finite or conjugated verb, and there is no inversion of order.
2)Direct object:
Who (or whom) did you see? (you: subject; who did see: predicate; who/whom: direct object)
3)Indirect object (introduced by the preposition to):
Who did you give the present to? (you: subject; who to: indirect object)
4)Objet to the preposition:
With whom did you go? / Who did you go with? (with: preposition; whom/who: object to the preposition)
5)Subjective complement:
Whose is that book? (that book: subject; whose: subjective complement)
6)Objective complement:
What did they make him? (what: objective complement; him: direct object)
The interrogative adjectives are: whose, what and which. They have an adjectival function.
Which books have you lent him? (you: subject; which books: direct object)
The direct object is a noun phrase (which books). Within the noun phrase, ‘books’ functions as the Head (the most important word) and ‘which’ pre-modifies books. ‘Which’ is an interrogative adjective.
Whose antiques are these? (these: subject; whose antiques: subjective complement, noun phrase)
Note:
Which (pronoun and adjective) is used instead of ‘who and what’ when the choice is restricted.
What will you have to drink? (general inquiry)
There’s whisky, gin and sherry; which will you have? (restricted choice)
