Which transitional word or phrase correctly begins the last sentence of this paragraph?

in his novel lord of the flies, william golding explores the idea that humans have an inherent impulse to be evil. the story is based on a group of children who are stranded on a deserted island. golding portrays them as normal, happy children having an adventure. they quickly become dehumanized and increasingly violent as the novel progresses.

a) although
b) moreover
c) however
d) in addition