Explanation
Correct answer: B.
Choice B is the best answer. The text tells us that the black-furred wolves are more common in areas with regular outbreaks of distemper virus and are more likely to be immune to distemper than the gray-furred wolves. This suggests that the gene variant that results in black fur may be linked to immunity to the distemper virus.
Why the other choices are wrong
Choice A
Choice A is incorrect. The text never compares North American gray wolves to other wolf species—in fact, it never discusses other wolf species at all, so there’s no basis for this inference.
Choice C
Choice C is incorrect. The life span of gray wolves is never mentioned in this text, so we have no basis for this inference.
Choice D
Choice D is incorrect. This is too extreme. The text says that "black-furred wolves are more likely to be immune to distemper than the gray-furred wolves," but that alone doesn’t mean that black-furred wolves will replace gray-furred wolves across North America.