Complete Question Explanation
Assumption. The correct answer choice is (A)
This remarkable Assumption question presented an early challenge on this LR section. The strong assumption required by the argument may have caught test-takers off-guard, but with clarity about the conclusion and the support offered, an accurate and precise prephrase is possible. In fact, this question is an excellent test of your understanding of the logical structure of LSAT arguments.
To wit, begin with the conclusion: The leopard magpie moth faces extinction.
Why?
- It feeds on a certain kind of grass.
- This grass makes it disgusting to predators.
- This grass faces extinction.
Let's engage with this argument on its merits. How could it be possible that the moth might not face extinction even though its grassy defense might disappear? Perhaps it could find another way to make itself unsavory. What's necessary for the author to conclude that this moth faces extinction because the grass faces extinction? The moth must not have another defense mechanism.
Answer choice (A): This is the correct answer choice. If you knocked this out because it referred to the "only" way the moth can make itself unpalatable to predators, don't beat yourself up. However, this actually is a necessary, unstated belief. Do the Assumption Negation Test. If there were another way the moth could make itself unpalatable, would it still face extinction? No. Therefore this is an assumption required by the argument.
Answer choice (B): Perhaps one of the most visually amusing LSAT answer choices of all time, this choice conjures up images of acrobatic caterpillars with daring escapes from ravenous birds. Unfortunately, it was not to be. Is it actually necessary that the Leopard Magpie Moth lack the the agility to escape any of its predators? No, perhaps it might be agile enough to escape from some sad, torpid toad.
Answer choice (C): A "who-cares" answer choice if ever there were one, this choice just fills up that awkward middle answer choice position. Among other problems, this answer choice brings in outside assumptions about visual cues for predators. It's also strongly worded and flunks the Assumption Negation Test.
Answer choice (D): Premised on a misreading of the premises, this is a terrific trap answer choice. This choice invites students to wonder whether the caterpillar might be able to find Natal grass even if this grass has become scarce. The problem is the Natal grass faces not just scarcity but
extinction. Even if the caterpillars have a Natal grass radar, it's not going to help them if the grass disappears.
Answer choice (E): Like (C), this is another "whoa that's a strong statement" answer choices. What if some of the predators have developed a tolerance to the toxin? Might the Leopard Magpie Moth still face extinction because of the absence of the Natal grass? Certainly. This answer choice comes out of left field, and you should send it back where it came from.
the moth isn't in danger of extinction. The problem there being that "some" is too vague and doesn't preclude the possibility that any one (or even multiple) predator would wipe it out.