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Difficulty: EasyStrengthening Arguments

Three months ago, a citrus orchard manager introduced a species of non-stinging predatory mite to combat Asian citrus psyllids, insects that transmit a destructive bacterial disease to orange trees. Over the subsequent three-month period, the population of Asian citrus psyllids in the orchard decreased by 60 percent. Based on this outcome, the manager concluded that the introduction of the predatory mites was responsible for the decline in the psyllid population.

Which of the following, if true, provides the strongest support for the manager's conclusion?

  1. A
    Right before introducing the predatory mites, the orchard manager applied a broad-spectrum chemical insecticide aimed at reducing insect pest populations.
  2. B
    Asian citrus psyllids cause significantly more harm to sweet orange trees than to lemon trees grown in adjacent fields.
  3. In nearby citrus orchards with identical environmental conditions where predatory mites were not introduced, the Asian citrus psyllid population did not decrease over the same three-month period.Answer
  4. D
    Deploying predatory mites requires specialized equipment that increases overall pest management costs compared to traditional chemical spraying.
  5. E
    The bacterial disease spread by Asian citrus psyllids leads to premature fruit drop and severely reduced harvest yields.

Answer

The argument is most strongly supported by the statement indicating that in nearby orchards under identical conditions where predatory mites were not introduced, the psyllid population did not decrease.
The conclusion asserts a causal relationship between introducing predatory mites and the 60 percent decline in psyllids. The correct choice provides a control comparison: in neighboring orchards where environmental conditions were identical but mites were absent, psyllid populations remained stable. This rules out seasonal changes, weather events, or natural population cycles as the cause of the decline, significantly strengthening the manager's claim that the mites were responsible.

Step-by-Step Solution

1
Identify the argument's premises and conclusion.
Premise: Mites were introduced, and psyllid numbers dropped by 60% over 3 months. Conclusion: Introducing the mites caused the drop in psyllids.
Understanding the precise cause-and-effect claim is necessary before evaluating strengthening evidence.
2
Analyze what evidence would strengthen a causal claim.
A causal argument is strengthened by ruling out alternative explanations (such as weather or pesticides) or showing a control scenario where the cause is absent and the effect does not occur.
Standard GMAT strengthening mechanisms for causal arguments rely on establishing correlation/control or eliminating competing causes.
3
Evaluate the option presenting a control group.
Showing that nearby orchards without mites experienced no decrease in psyllids under identical weather conditions confirms that the decline was specific to the orchard with mites.
This effectively rules out external weather/seasonal factors as the true cause of the population decline.

Key Concept

Strengthening Causal Arguments via Control Groups and Alternative Cause Elimination
Estimated Time:1m 15s
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Topics

Strengthening Arguments

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