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Difficulty: HardWeakening Arguments

To reduce municipal expenditures on stormwater drainage maintenance, the city of Oakhaven recently replaced non-native turf along major roadways with deep-rooting native shrubs known to absorb large volumes of groundwater. City officials reasoned that because these shrubs absorb up to 40 percent more groundwater during severe storms than non-native turf, storm runoff entering the municipal drainage network will decrease substantially, thereby lowering ongoing maintenance costs over the next decade.

Which of the following, if true, most seriously weakens the city officials' argument?

  1. The deep root systems of the mature native shrubs expand into subterranean drainage pipes, causing structural blockages that require repairs far more costly than routine drainage maintenance.Answer
  2. B
    Non-native turf species generally require higher amounts of chemical fertilizers and frequent mowing compared to native shrub species.
  3. C
    neighboring municipalities have successfully implemented similar green infrastructure initiatives using native tree species rather than shrubs.
  4. D
    Initial nursery acquisition costs for the native shrubs were higher than the cost of replacing the existing turf with new non-native turf.
  5. E
    Severe storms in Oakhaven are projected to increase in frequency over the next ten years.

Answer

The argument is most seriously weakened by the finding that the deep root systems of the mature native shrubs expand into subterranean drainage pipes, causing structural blockages that require repairs far more costly than routine drainage maintenance.
The correct answer identifies a direct, unintended side effect of the planted native shrubs: their deep roots cause subterranean pipe damage requiring repairs that exceed routine maintenance costs. Because the total financial burden will increase rather than decrease, this fact directly invalidates the city council's conclusion.

Step-by-Step Solution

1
Deconstruct the argument structure
Premise: Native shrubs absorb 40 percent more groundwater during storms than non-native turf. Conclusion: Replacing turf with native shrubs will lower municipal stormwater drainage maintenance costs over the next decade.
Identifying the premise-to-conclusion link isolates the core assumption: that reducing runoff volume is the sole factor determining overall drainage maintenance costs.
2
Identify the unstated assumption and logical vulnerability
The argument assumes that planting native shrubs will not create new, unexpected costs that outweigh the maintenance savings from reduced storm runoff.
In plan-to-goal feasibility arguments, a common vulnerability is an unconsidered negative side effect that prevents the goal (cost savings) from being realized.
3
Evaluate options for information that undermines the assumption
The option describing root intrusion into underground drainage pipes shows that the shrubs cause severe pipe blockages, generating repair expenses greater than the original maintenance budget.
Demonstrating that the plan creates higher maintenance costs directly shatters the conclusion that overall maintenance spending will decrease.

Key Concept

Evaluating Plan Feasibility and Unintended Side Effects in Causal Arguments
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Topics

Weakening Arguments

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