Logical ReasoningDifficulty: Hard

PT128 S2 Q13 Explanation

Scientist: There is little doubt

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsMain Conclusion

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Stimulus

Scientist: There is little doubt that the ice ages were caused by the unusually rich growth of vegetation worldwide. Since vegetation converts carbon dioxide into oxygen, excessive vegetation would have depleted the carbon dioxide in the atmosphere. Carbon dioxide helps the atmosphere retain the sun's the earth cools significantly, thereby causing an ice age.

What this question is testing

Main Conclusion

Your task

Break the argument into its conclusion and evidence, then do exactly what the question stem asks with that structure.

Common trap

Answers that sound relevant to the topic but don't connect to the argument's actual reasoning.

Winning move

Predict what a right answer must do, then test each choice against the conclusion-evidence gap.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
13.

Which one of the following most accurately expresses the main conclusion of

Answer choices

  1. Summary, not a Conclusion9% picked this

    Excessive growth of vegetation worldwide could have caused one or more ice ages by depleting the carbon

    This isn't a good match for the first sentence, because the first sentence doesn't even mention CO2 in the atmosphere. This is trying to provide a summary of the entire paragraph, whereas we were asked simply to identify the conclusion. Also, the conclusion is saying "ALL the ice ages" were caused by rich growth of vegetation worldwide, whereas this answer choice is only talking about "one or more ice ages".

  2. Bad Match13% picked this

    If the carbon dioxide in the atmosphere is depleted, the earth cools significantly, thereby causing

    This isn't a good match for the first sentence, because the first sentence doesn't even mention CO2 in the atmosphere.

  3. Bad Match3% picked this

    An excessive growth of vegetation causes the carbon dioxide in the atmosphere

    This isn't a good match for the first sentence, because the first sentence doesn't even mention CO2 in the atmosphere.

  4. Bad Match6% picked this

    If unusually rich growth of vegetation caused the ice ages, it undoubtedly did so by depleting the carbon

    The first sentence isn't a conditional. The author says that rich growth of vegetation caused the ice ages. Period. There isn't anything about CO2 in the first sentence.

  5. Correct69% picked this

    Unusually rich growth of vegetation worldwide was almost certainly the cause of

    Why this is right

    This matches the first sentence, which all the other ideas supported.

    Skill tested: Main Conclusion · how this choice captures the argument's function is the move to repeat next time.

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