Logical reasoning PrepTest 149 · Section 3 · Question 8

Incorrect. The relative number of plant species on the mainland and on islands is immaterial to the argument because the phenomenon is specifically noted as being about the rate of extinction instead of the number of extinct plants.

Incorrect. The stimulus compares the rate of extinction of plants native to the mainland and native to island. Plants that are native to the mainland but move to islands aren't specifically noted and so are out of scope.

Incorrect. This answer establishes an alternative explanation for the extinction, thus weakening the argument.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Phenomenon Ð Plant species on islands are going extinct faster than on the mainland
Explanation Ð Island plants haven't adapted protections against large land mammals
Support Ð Land mammals don't make it to islands until after humans show up

Answer Anticipation:
This argument falls into the phenomenon/explanation pattern, and those generally have answers that address alternative explanations. In a Strengthen question, we can eliminate an alternative explanation to strengthen the one from the stimulus. It'd be enough to head to the answers with this anticipation, but it's very generic and might miss a specific answer. However, there are two aspects of this stimulus that can allow us to get a more specific anticipation.

Phenomenon/explanation passages are generally causal, and that's no different here. The cause of the island plant extinctions is noted to be large land mammals. However, the premise brings in another concept—humans. If the humans are bringing the mammals, that suggests an alternative cause—the humans themselves could be causing the extinctions directly, or through some means other than bringing large land mammals with them.

All of this is circling around the same idea—alternative causes/explanations. However, we should be particularly cognizant of answers that bring in humans, as they're a part of the only premise and aren't immediately referenced in the conclusion.

Answer Explanation:
This answer is interesting in that it seems to suggest an alternative cause—humans. However, the premise specifically notes that humans are the cause of the land mammals making it to the islands. So while this answer does tie the extinctions to the human colonization of the islands, that also ties it to the presence of large land mammals. In short, this answer makes it likely something about humans is resulting in the plant extinctions, and that includes the presence of land mammals, strengthening that possibility relative to other possibilities that aren't related to human habitation. And relatively strengthening a possibility is still strengthening it.

Key Takeaway:
Phenomenon/explanation passages generally have answers that address alternatives, either directly or indirectly. When two potential explanations are tied together—here, humans and large land animals—be careful about answer choices that provide evidence for one, as it might also provide evidence for the other.

Incorrect. Once they're on an island, they may not have an option. Additionally, a preference doesn't determine all action. We prefer ice cream to broccoli, but we still eat the latter quite frequently.