Answer
b. He doesn't take pleasure in killing another person.
Explanation
Rainsford's lack of a smile after defeating Zaroff reflects his discomfort and ethical conflict with taking pleasure in the demise of another person, even in a survival scenario. Throughout the story, Rainsford experiences the horrors of being hunted, which fundamentally changes his perspective on killing for sport, something he and Zaroff initially shared enthusiasm for. His statement, "I am still a beast at bay," suggests he feels cornered and compelled to act in ways that go against his inherent values, emphasizing his reluctance and emotional turmoil rather than satisfaction from his victory.