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Question

Difficulty: MediumStrengthening Arguments

Municipal planners in City K recently installed permeable asphalt along downtown sidewalks to reduce surface runoff during storm events. During the first rainy season following installation, measured runoff volume entering the local river decreased by 30 percent compared to the historical seasonal average. The planners concluded that expanding the installation of permeable asphalt throughout all municipal districts will significantly mitigate urban flooding during future severe storms.

Which of the following, if true, provides the strongest support for the municipal planners' conclusion?

  1. The total volume and intensity of rainfall during the first rainy season were typical of severe storm conditions, and no other runoff control measures were introduced in the downtown area during that period.Answer
  2. B
    Sediment accumulation in permeable asphalt pores gradually decreases its water filtration capacity after repeated heavy rainfall events.
  3. C
    Permeable asphalt is produced using recycled aggregate materials that lower the city's overall carbon emissions relative to conventional paving materials.
  4. D
    Neighboring cities that implemented permeable asphalt reported that routine maintenance costs exceeded initial budget forecasts.
  5. E
    Surface runoff volume into local rivers is the primary metric mandated by state regulators for evaluating municipal environmental compliance.

Answer

The argument is most strongly supported by the statement showing that the total volume and intensity of rainfall during the trial period were typical of severe storm conditions and that no alternative runoff control measures were active.
The correct answer strengthens the argument by demonstrating that the test period was representative of severe storm conditions and by ruling out alternative explanations (such as other flood control projects or light rainfall) for the observed reduction in runoff.

Step-by-Step Solution

1
Deconstruct the argument into premise and conclusion.
Premise: Permeable asphalt installed downtown coincided with a 30% drop in river runoff during one rainy season. Conclusion: Expanding permeable asphalt citywide will significantly mitigate future urban flooding.
Identifying the gap between a single limited trial and a broader causal claim is essential for evaluating strengthening statements.
2
Identify potential vulnerabilities in the author's reasoning.
The 30% drop could have been caused by lighter-than-usual rain or other unmentioned flood control interventions, or the trial conditions might not represent true severe storm conditions.
Strengthening questions often require ruling out alternative causes or confirming that trial conditions mirror the target conditions.
3
Evaluate the choices to find the statement that addresses these vulnerabilities.
Confirming that rainfall intensity matched severe storm conditions and that no other interventions occurred eliminates confounding variables and supports the claim that permeable asphalt caused the reduction.
Ruling out confounding variables directly increases confidence in the causal relationship asserted by the conclusion.

Key Concept

Strengthening Arguments by Ruling Out Confounding Variables
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Topics

Strengthening Arguments

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