The answer is D, practices.
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'd have to know the story to answer it 100% correct... but one answer could be "A" if marjorie is not socially accepted herself. But it could also be "D" if Bernice was tempted not to cut her hair.
