Who, whom, which, and what are pronouns. a. only interrogative b. reflexive c. relative and interrogative d. only relative

They are relative and interrogative pronouns. It just depends on their place in the sentence. If they are written in the beginning of a sentence and directly related to the question issue, they are in position of an interrogative pronoun.

Example: Who is that lady?

But, if they are inside a sentence, creating a relation with a previous spoken noun, they are relative pronouns.

Example: That lady, who has got a brown dog, is my new neighbour.

b is the correct answer