D. Is for sure the answer because it leaves you hanging without a complete thought.
Mustapha Mond is the most powerful and intelligent proponent of the World State. ... Mustapha Mond is a paradoxical figure. He reads Shakespeare and the Bible and he used to be an independent-minded scientist, but he also censors new ideas and controls a totalitarian state.
Synonyms of nonchalant
daily, effortless, free-and-easy, passing(a), fooling, chance(a), cursory, insouciant, occasional, perfunctory, casual, everyday.
I think it is sentence D. Hope this helped<span />