In that case, would đáp be the classifier for đáp án? or would câu work here? or does it just not use a classifier?
"đáp án" goes together as a whole so there is no classifier. In very informal case, "cái" can be used as classifier for "đáp án".
This might be a dumb question but what does "câu" do to this sentence? I either forgot or missed something on mobile.
it nominalizes the verb trả lời (to answer) into a noun (an answer). many consider it a classifier denoting sentences, expressions, lines.
I thought that "trả lời" was the VERB form of "answer" and "đáp án" was the NOUN. In this sentence, "answer" is a noun, so should be "đáp án".