b-
Interrogate pronouns encompass "what, which, who, whom, whatever, whomsoever, whoesever, whichever, when, how, why and where etc. Of these which, what and whose indicate interrogative determiners as they can't stand on their own, needing a noun to be modified in order to make sense. For a visual, compare "what lectern are you buying" & "what are you buying". In the latter, the noun is preceded by what, which indicates a modifying relationship and therefore its removal results in a different meaning, akin to what is conveyed in the latter instance. Interrogative pronouns that are actually interrogative adverbs are why, where, when and how. That's mostly on account of these words calling for an adverbial phrase as a means of an answer e.g.: how shall we do? you should do it like this