Answer:
A. what
Explanation:
Interrogative pronouns are the type of pronouns used to pose direct or indirect question. They may refer to either objects or people or both.
Main interrogative pronouns are who, what, which, whom and whose.
In direct questions, they are always in the beginning of the sentence which makes them easy to identify:
Who did that?
In indirect question they are in the beginning of the dependant clause:
I wonder what happened here.
