The correct answer is: Zaroff has no conscience, while Rainsford does have a conscience.
General Zaroff has no concern or compassion for human life, he does not believe that the hunting of humans is wrong therefore he would feel no guilt in taking the life of another for sport and has no conscience. Rainsford on the other hand does have a conscience and despite having seen the brutalities of war he sees the hunting of humans as cold blooded murder. He has compassion and empathy towards others and could never justify taking a life for such reasons as sport.