Answer Choice A is correct, because part of McKinnon’s argument depends on the fact that Ceres has a low density, which is rare for an asteroid but “closely matches Pluto and other icy objects native the outer solar system.” Answer Choice A says, “the average density of Pluto is similar to that of Ceres,” which would support his argument. Answer Choice B is incorrect because nothing in McKinnon’s argument depends on Ceres’s and Neptune’s relative distances from the Sun. Answer Choice C is incorrect because, although part of McKinnon’s argument depends on Ceres having a greater mass than other objects in the asteroid belt, like Juno, Answer Choice C emphasizes that Ceres is “only slightly greater” in mass, which wouldn’t provide strong support, especially relative to Answer Choice A, and also confuses mass and size. Answer Choice D is incorrect, because McKinnon’s argument doesn’t depend on Ceres having a greater density than either Neptune or Uranus, but on it having a lower density than other objects in the asteroid belt.
How to solve this? The Question asks, “Which data presented in the table would McKinnon find most useful to his argument?” Before looking at the answer choices and attempting to solve this question, we should first remind ourselves of McKinnon’s argument. If we scan for his name, we find him mentioned in Paragraphs 2 and 3 (Lines 8-24). Here, we can trace the core features of his argument: (1) that Ceres “is by far the largest object in the asteroid belt” (Lines 8-9); (2) that Ceres has a low density and is made of 25 to 30 percent water, which is “a high proportion for an asteroid, but closely matches Pluto and other icy objects native to the outer solar system; (3) that Ceres may have ammonium-rich clay at its surface. Only these three core features can be relevant to the Question, and we should expect the correct answer to reference one of them.
Answer Choice A says, “the average density of Pluto is similar to that of Ceres.” This answer choice mentions density and the fact that Pluto and Ceres have similar densities, which does match McKinnon’s second point, so we should keep this option. Answer Choice B says that “Neptune is located much farther from the Sun than is Ceres.” Because McKinnon’s argument doesn’t mention distance from the Sun or how Neptune and Ceres compare in that regard, we can eliminate this option. Answer Choice C says that “the mass of Ceres is only slightly greater than that of Juno.” Because the table tells us that Juno is an asteroid, his answer choice may seem to reference McKinnon’s first point, that Ceres “is by far the largest object in the asteroid belt,” so we can keep this option (although we may notice some issues with upfront). Answer Choice D says that “Ceres is denser, on average, than either Neptune or Uranus.” This answer choice mentions density, like McKinnon’s second point, but doesn’t make the same claim that he does — that Ceres has a low density similar to Pluto and unlike other objects in the asteroid belt — but instead mentions the density of Ceres relative to Neptune or Uranus, so we can eliminate this option.
Now, we have to decide between Answer Choices A and C, and should focus on looking for the error in one of them that will allow us to weigh their relative strengths and weaknesses. If we look at Answer Choice C, we can notice two issues with it. One, it emphasizes that the mass of Ceres is “only slightly greater” than that of Juno, which wouldn’t provide strong support for McKinnon’s claim that Ceres is “by far the largest object in the asteroid belt.” Two, it confuses the properties of mass and size, which are related but not identical. So, we should choose Answer Choice C.