PrepTest 102

[lcid:3506] Prep Test 102 LSAT — Logical Reasoning — S3 Logical reasoning

Question prompt

Ornithologist: The curvature of Remaining source text redacted.
Why the credited answer is right

Credited answer: B

The notes below walk through why it fits the stem and how to eliminate the rest.

Argument or Facts

Argument/Argument

Valid or Flawed

Flawed/Flawed

Question Type

Strengthen with Necessary Premise Questions

Stimulus Summary

O: Modern tree-dwelling birds have claws that let them perch, and so did Archaeopteryx, so Archaeopteryx must have been tree-dwelling. P: Chickens perch in trees but are ground-dwelling, so the ability to perch isn’t good evidence of being tree-dwelling.

Answer Anticipation

This question tasks us with finding a necessary premise to the Ornithologist’s argument, so we can focus there instead of on the Paleontologist’s response. Looking at that argument, we can see that it’s one based on comparisons. The Archaeopteryx has claws with similar curvature to modern tree-dwelling birds. That curvature allows the modern birds to perch on trees, but it’s only noted that it “must have” enabled the Archaeopteryx to do so. That’s an inference, not a statement of fact, so we have our first assumption - that the Archeopteryx used the curvature for a similar purpose as the modern birds. Based on this similarity, the argument then assumes another similarity - that both sets of birds were tree-dwelling. However, there’s no indication that even if the Archaeopteryx used the curvature of its claws to perch in trees that it therefore lived in trees (as the Paleontologist pointed out). So we have two assumptions that we can look for the in the answers: The Archaeopteryx used the curvature of its claws to perch in trees (similar to modern tree-dwelling birds) Birds that can perch in trees are tree-dwelling

Answer choices

  1. A
    Modern tree–dwelling birds are Remaining source text redacted.
    Why choice A is not credited
    The birds don’t have to be related for similar structures to have similar functions.
  2. B
    Archeopteryx made use of Remaining source text redacted.
    Why choice B matches the stem
    This answer matches with the first assumption we noted. The argument states that the Archaeopteryx had similarly curved claws to some modern birds, and it therefore must have used them for the same purpose. That assumes that it did make use of that curvature. If it didn’t, then we can’t assume they perched in trees and thus have no reason to believe they were tree-dwelling - the argument falls apart. This answer is therefore a necessary premise.
  3. C
    There have never been Remaining source text redacted.
    Why choice C is not credited
    This answer is too extreme in stating that there have “never” been tree-dwelling birds without curved claws. Additionally, the relevant situation would be birds with curved claws who weren’t tree-dwelling.
  4. D
    Archeopteryx was in fact Remaining source text redacted.
    Why choice D is not credited
    That was a throwaway fact unrelated to the argument/similarities between the Archaeopteryx and modern birds, so this answer is incorrect.
  5. E
    The curvature of the Remaining source text redacted.
    Why choice E is not credited
    If there were other evidence, that would only serve to strengthen the Ornithologist’s argument, so this isn’t a necessary premise.

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