Logical ReasoningDifficulty: Easy

PT143 S4 Q17 Explanation

Near many cities, contamination

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

TopicsRole

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Stimulus

Near many cities, contamination of lakes and rivers from pollutants in rainwater runoff exceeds that from industrial discharge. As the runoff washes over buildings and pavements, it picks up oil and among the biggest water polluters.

What this question is testing

Role

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
17.

The statement that contamination of lakes and rivers from pollutants in rainwater runoff exceeds that from industrial discharge plays which one of the following

Answer choices

  1. Reversed Roles2% picked this

    It is a conclusion for which the claim that water itself should be considered a polluter

    It makes more sense to say the 1st sentence supports the 3rd, than to say that the 3rd supports the 1st, as this answer is claiming. We can ask ourselves which of these feels better: Why should I believe that ... "Contamination of lakes and rivers from pollutants in rainwater runoff exceeds that from industrial discharge"? Because -- water itself is among the biggest water polluters. or Why should I believe that ... "Water itself is among the biggest water polluters"? Because -- Contamination of lakes and rivers from pollutants in rainwater runoff exceeds that from industrial discharge. The 2nd one feels more natural. The fact that pollutants from rainwater runoff exceeds pollutants from industrial discharge sounds like support for the idea that water is among the biggest polluters.

  2. Bad Conclusion Match8% picked this

    It is cited as evidence that pollution from rainwater runoff is a more serious problem than

    It is definitely evidence, but the conclusion is the final sentence: "water is among the biggest water polluters". According to this answer, the conclusion is some imaginary claim never said that "rainwater runoff is a more serious problem than industrial discharge".

  3. Weak Match5% picked this

    It is a generalization based on the observation that rainwater runoff picks up oil and other pollutants as it

    Is tough to pinpoint the precise reason this is wrong. The 2nd sentence definitely helps us to understand how rainwater runoff could be a source of pollutants, but it feels wrong to say that a scientific measurement of whether pollutants from rainwater exceed that from industrial discharge is based on the observation that runoff picks up pollutants. Such a measurement would be based on actually tallying up types / amounts of pollutants. The 2nd sentence gives us the causal mechanism by which to understand how the 1st sentence could be true, but the 1st sentence isn't based off that observation.

  4. Correct84% picked this

    It is a premise offered in support of the conclusion that water itself is among

    Why this is right

    Well, this is just straightforward and pure. We can't argue with the fact that it's a premise (intermediate conclusions are also premises), and we can't argue with the fact that the conclusion was the final sentence. Where we might have to work hard to make other answers work, this one requires no work.

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

  5. Wrong Purpose1% picked this

    It is stated to provide an example of a typical kind

    It was not stated for the sake of providing a typical kind of city pollution. It was stated to support the comparative conclusion that water is one of the biggest polluters.

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