B, D, and E all support this claim.
B, because Rainsford is incredulous at the concept of Zaroff hunting humans; he believes it is a grotesque joke at his expense. D, because he calls the hunting of humans outright cold-blooded killing, showing his contempt for the subject. This leads into the reasoning for E; E shows that he is against hunting humans because he directly states that the hunting of humans is cold-blooded murder, and he does not condone it in the slightest. This is accentuated by his stiff tone.