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.
I believe the correct answer is A. burst
A noun phrase denoting a person or thing that is the recipient of the action of a transitive verb, for example the dog in Jimmy fed the dog.
Hope this helps!
