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Question

Difficulty: MediumWeaken

Agronomist: In field trials across several arid test sites, cereal crops treated with a newly developed mycorrhizal fungal bio-fertilizer yielded 30 percent more grain per acre than crops treated with standard chemical fertilizers. Because the formulation enhances root nutrient uptake and soil moisture retention without depleting organic matter, switching exclusively to this bio-fertilizer will significantly increase overall grain production across the nation’s drought-prone farming regions.

Which of the following, if true, most seriously weakens the agronomist’s argument?

  1. A
    Crops cultivated with the mycorrhizal bio-fertilizer exhibited substantially greater tolerance to sudden heat waves than crops fertilized with conventional chemical blends.
  2. B
    In preliminary laboratory trials prior to the field studies, the bio-fertilizer failed to enhance soil moisture retention in synthetic sand mixtures.
  3. Commercial grain growers in the nation's drought-prone regions routinely treat their fields with broad-spectrum chemical fungicides that kill mycorrhizal fungi.Answer
  4. D
    Standard chemical fertilizers are completely incapable of enhancing root nutrient absorption in any soil environment.
  5. E
    Farms transitioning to the fungal bio-fertilizer will need to clean standard machinery before storing harvested grain.

Answer

The statement indicating that commercial growers in drought-prone regions routinely apply broad-spectrum fungicides that destroy mycorrhizal fungi is the correct answer.
The correct answer demonstrates that an established, widespread agricultural practice in the target regions (routine broad-spectrum fungicide application) directly destroys the active mycorrhizal fungi. This prevents the bio-fertilizer from functioning effectively on commercial farms, directly undermining the conclusion that adopting it will increase overall grain production across those regions.

Step-by-Step Solution

1
Identify the premises and the main conclusion of the stimulus.
Premises: Field trials showed a 30 percent grain yield increase with the fungal bio-fertilizer, and the formulation improves moisture retention and nutrient uptake. Conclusion: Switching exclusively to this bio-fertilizer will significantly increase overall grain production across the nation's drought-prone farming regions.
Understanding the structure isolates the logical leap from controlled trial results to nationwide commercial implementation.
2
Identify the unstated assumption linking the premises to the conclusion.
The author assumes that the conditions and practices present on commercial farms in these drought-prone regions will permit the bio-fertilizer to function as effectively as it did in the experimental trials.
Weaken questions require identifying unstated assumptions vulnerable to counter-evidence.
3
Evaluate the answer choices for new information that undermines this core assumption.
The statement regarding routine fungicide use shows that standard local practices will neutralize the active biological agent, preventing the bio-fertilizer from producing the promised yield gains.
An operational conflict between real-world farming practices and the biological mechanism directly breaks the link between trial performance and nationwide yield improvement.

Key Concept

Identifying hidden real-world implementation barriers that invalidate extrapolating experimental trial results to broad operational deployment.
Estimated Time:1m 15s
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Weaken

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