Logical reasoning PrepTest 143 · Section 4 · Question 21

Incorrect. While this answer does establish that porous outer bones aren't a characteristic shared by every deep diving species, it doesn't call into question whether it's a characteristic that only shows up in deep diving species, which would weaken the argument.

Incorrect. Without information about whether these reptile species are deep divers, this answer doesn't provide enough to analyze its impact and thus we can eliminate it.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
Modern deep-diving animals have porous outer bones. The ichthyosaur also had porous outer bones, so it was a deep diver.

Answer Anticipation:
This argument uses a similarity between modern deep-diving marine mammals and the ancient marine reptile the ichthyosaur—they have porous outer bones—in order to conclude that they're similar in another way—they are deep divers. And while porous outer bones are connected to deep diving—they allow the animal to surface—it's not established that only deep divers have these porous outer bones, or that it's a determining characteristic of deep divers.

As such, any relevant difference between ichthyosaurs and deep divers or anything that calls into question whether this point of comparison (porous outer bones) is relevant to the determination of whether an animal is a deep diver will weaken this argument. Since we already know one difference between the modern deep-diving marine mammals and the ichthyosaur, a reptile, the correct answer could connect to this detail.

Answer Explanation:
This answer establishes that most marine reptiles that weren't deep divers have porous outer bones. If that's the case, then the porous outer bones—at least in reptiles—aren't a good way to determine if an animal is a deep diver, and thus the conclusion is weakened.

Key Takeaway:
Arguments that rely on similarities to draw a comparison about another similarity frequently have correct answers in Weaken questions that establish a relevant difference between the elements in the comparison. However, the argument is also assuming that the similarity raised is relevant to the determination, so answer choices that call the relevance or applicability of that comparison into question can also weaken the argument.

Incorrect. First, this answer just deals with a single example of a modern deep-diving marine mammal, whereas the stimulus was about them as a group, so this answer is relatively weak and wouldn't have much of an impact on the argument. Additionally, a lack of clear evidence ichthyosaurs had these features doesn't establish that they didn't—maybe the characteristics of whales are all behavioral and thus impossible to view in an extinct animal.

Incorrect. If anything, this answer aligns with the argument.