Logical reasoning PrepTest 127 · Section 1 · Question 7

Question prompt

Two different dates have Remaining source text redacted.
Why the credited answer is right

Credited answer: E

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

Argument or Facts

Facts

Valid or Flawed

NA

Question Type

Must Be True Questions

Stimulus Summary

The same soil samples were tested for two things to determine when the last North American ice age ended:
Beetle fragments to see when warmth-adapted beetles replaced cold-adapted ones (more than 500 years earlier) Pollen grains to see when ice moved out and spruces moved in (more than 500 years later)

Answer Anticipation

This stimulus is interesting in that it can seem more like a separate question type instead of a Must be True question. It’s similar to a Paradox question in that the situation described seems to be contradictory. It could also be viewed as fitting into a flaw-based question, as it uses a “proxy” measurement - it doesn’t measure the end of the ice age directly, but rather through beetle and pollen remains.
However, this is a Must be True question, so we should focus on finding an answer that follows from the information in the stimulus. There, the “same [soil] samples” were tested for two separate things that would be associated with the end of an ice age.
First, beetle fragments were tested. The researchers looked at when cold-adapted beetles (thus living in the ice age) died off and warmth-adapted beetles (thus living after the ice age) moved in. This gave one date. Then, pollen grains were tested to see when the ice moved out and the spruce trees moved in. This gave another date more than 500 years later.
Since these two things were measured from the same soil sample, it must be the case that the ice age ended at that location at one time. Since these dates are far apart, but they both highlight something that would have happened after the ice age ended, it must be the case that the beetles moved in faster than the spruces were able to regrow in the area. That would explain the different dates based on remains found in the same soil.

Answer choices

  1. A
    Toward the end of Remaining source text redacted.
    Why choice A is not credited
    The warmth-adapted beetle fragments and pollen grain suggesting the growth of spruce trees were found in the same area after the ice age ended, so, if anything, there’s evidence against this answer.
  2. B
    Among those sediments deposited Remaining source text redacted.
    Why choice B is not credited
    The soil samples tested had both cold-adapted beetle fragments (otherwise the shift from them to the warmth-adapted ones couldn’t be seen) and spruce pollen, but that doesn’t mean that this is standard (“expected to contain”) for soil samples from that time period. The samples in question may serve as the basis for the analysis because they were unique in having these remains.
  3. C
    Ice masses continued to Remaining source text redacted.
    Why choice C is not credited
    This answer is trying to get you to think that the 500-year difference is explained by the glaciers continuing to advance between the beetles moving in and the spruce trees growing, but there’s no indication that’s the explanation for it. In fact, the warmth-adapted beetles likely wouldn’t have moved in without the glaciers being gone.
  4. D
    The species of cold–adapted Remaining source text redacted.
    Why choice D is not credited
    Those beetles disappeared from the given areas, but that doesn’t mean they died out - they could have retreated with the glaciers to colder areas.
  5. E
    Toward the end of Remaining source text redacted.
    Why choice E matches the stem
    This answer provides the resolution that makes sense based on the data. The same soil samples showed that warmth-adapted beetles moved into a given area 500 years before the spruce trees showed up, supporting this answer that the beetles moved in faster than the trees.

What this tests

Question analytics

Based on historical answer selection rates for this question.

Answer choice distribution

  1. A 8%
  2. B 13%
  3. C 9%
  4. D 7%
  5. E Credited 63%

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