The answer is C. Conceptual. The blank is supposed to be a describing word, in other words, and adjective. So, conceptual describes the artist. Therefore your answer is C!
The significance of this quote is Montag's realization of what his job is actually about and what it implies. He became a fireman because he was meant to. However, he is now haunted by this new feeling and does not know anymore what is right and what is wrong.
