26.R.9 & 27.R.9 (medium)
Answer Choice C and Answer Choice D are the correct answers here, because Lines 49-53 say that “Bottke and Levison’s computer simulations show that the observed number of objects is about right if they are immigrants, though they have assumed many of the objects broke up after transport,” which gives us an assumption on which their conclusions depend s(objects broke up after transport) and which, if shown to be wrong, would weaken their study. Answer Choice C follows this line and says the study would be weakened if it was “demonstrated that very few objects broke up after migrating to the asteroid belt.” For Question 26, Answer Choice A is wrong, because the confirmation that “heat from the Sun burned away the outer layers of all immigrant objects” would support their conclusion. Answer Choice B is wrong, because their argument doesn’t depend on the fact that objects in the inner solar system were stable. Answer Choice D is also wrong, because their argument also doesn’t depend on the fact that all objects in the outer solar system survived in the asteroid belt today.
How to solve this? Question 26 asks us what kind of study would most weaken Bottke and Levison’s conclusions. To solve this, we should have a basic understanding of their so we can predict and identify studies that would contradict or undermine it. Bottke and Levison’s main claim (in the fifth paragraph), is that some objects from the outer solar system orbit in the asteroid belt, and can be identified by a specific residue which would be expected to form as their outermost layer was vaporized by the sun. They also claim that the numbers of observed objects add up on this theory, although they make an adjustment based on an assumption that many objects broke up after traveling across the solar system. From here, we should go through the answer choices for Question 27, looking for a text that could suggest a possible weakness in their argument. This might be a specific claim that their conclusion depends on, but is likely to also be an assumption they make. So, we may not be able to identify the text perfectly, but we can probably eliminate some options and begin to pinpoint the direction of this Question.
For Question 27, Answer Choice A tells us that Bottke and Levison led a pair of studies to support their claim. Because this a more factual and introductory claim, without any details of their conclusion contained within it, we should discount against it. Answer Choice B tells us that they focused on two specific types of asteroids, “the so-called D- and P- type asteroids.” Our answer might involve this specific claim of their argument, so we shouldn’t eliminate it, but it also doesn’t provide us any rhetorical cue that this is an especially important aspect of their argument or that likely to be weak, so we shouldn’t expect it will be our answer either. Answer Choice C tells us about these asteroids they studied, the residue they contained and why they’re expected to contain this residue. We should treat this answer choice like the previous one and not eliminate it but also not expect too much of it either. Answer Choice D says that Bottke and Levison’s computer simulations support their conclusion, but that this relies on an assumption that many objects broke up after transport. This has the benefit of being both a central claim of their argument and also containing a rhetorical cue that indicates a possible weakness in their argument, because their conclusion relies on an assumption. We should keep these three options in mind, with Answer Choice D as the strongest candidate, and go to the answer choices for Question 26.
Answer Choice A says that their conclusions would be weakened by a study that “confirmed that heat from the Sun burned away the outer layers of all immigrant objects.” This choice contains a relevant topic, the sun burning away an outer layer, but gives us a claim that would support their conclusion, so we should eliminate it. Answer Choice B mentions a study that establishes “that the orbits of certain objects of the inner solar system were once less stable,” which doesn’t relate to any of our texts or Bottke and Levison’s conclusion, so we should eliminate this option. Answer Choice C says mentions a study that would demonstrate “that very few objects broke up after migrating to the asteroid belt.” This relates to our text from Answer Choice D, and would show the assumption they use to support their conclusions to be unfounded, which would weaken their argument. So, we should keep this option. Answer Choice D mentions a study that would prove “that not all immigrants from the outer solar system survive in the asteroid belt today.” Because Bottke and Levison’s conclusion doesn’t depend on the survival of all object from the outer solar system in the asteroid belt (in fact, it claims the opposite), we should eliminate this option. Thus, we should choose Answer Choice C and Answer Choice D.