GMAT Focus EditionVerbal ReasoningHard
A small town relies heavily on its fishing industry. Recently, a new factory opened upstream, and shortly thereafter, local fishermen reported a significant decrease in fish catch. They conclude that the factory's operations are polluting the river and causing the decline in fish populations. Which of the following, if true, would most seriously weaken the fishermen's conclusion?
- ALocal conservationists have long warned about overfishing in the river.
- BFish populations in other, unpolluted rivers in the region have also experienced similar declines.
- CThe factory produces goods that are essential for the town's economy, providing many jobs.
- DThe factory uses advanced wastewater treatment systems that meet or exceed all environmental regulations.
Show answer & explanationAnswer & explanation
Correct answer: B. Fish populations in other, unpolluted rivers in the region have also experienced similar declines.
The fishermen conclude a direct causal link between the factory and the fish decline. If similar declines are observed in unpolluted rivers, it suggests a broader, regional factor is at play (e.g., climate change, natural cycles), rather than the factory's pollution, thus seriously weakening their conclusion.
Why the other options are wrong
- A. Overfishing is an alternative cause, but the timing (decline *shortly after* factory opened) makes the factory a more immediate suspect. Option B provides a stronger, broader alternative that affects multiple rivers, making it more compelling.
- C. This addresses the economic impact of the factory, not whether its operations are causing the fish decline.
- D. Meeting regulations doesn't guarantee zero impact, and 'advanced' doesn't mean 'perfect,' so this weakens the argument slightly but doesn't rule out *any* pollution effect.
Ruling Out Specific Causation
To rule out a specific cause for an observed effect, provide evidence that the effect occurs independently of the proposed cause or is attributable to a broader, alternative factor.
- Look for confounding variables.
- Compare with control groups/areas.
- Consider broader trends or patterns.
Memory trick: When a direct link is claimed, scan the whole field, or the real cause will remain unnamed!