Necessary AssumptionDiff: Hardest
Logic Breakdown
Passage Summary: Scientists blame pollution for disappearing frogs, but because frog numbers naturally go up and down with the weather anyway, we can't be sure pollution is the real culprit.
Conclusion: It is impossible to prove for certain that industrial pollution is the cause of the recent decline in certain amphibian populations.
Reasoning: Most amphibian populations naturally fluctuate significantly from year to year due to changes in the weather.
Analysis: The author assumes that the 'natural variations' caused by weather are indistinguishable from the 'dramatic' declines attributed to pollution. To make the argument work, the author needs it to be true that the current decline isn't so massive or unique that it exceeds what weather could reasonably cause. If the current decline were 99% of the population and weather only ever caused a 10% dip, we *could* be fairly sure pollution (or something else) was at play. Look for an answer that bridges the gap by suggesting the recent decline falls within the realm of what natural variation might explain.
Conclusion: It is impossible to prove for certain that industrial pollution is the cause of the recent decline in certain amphibian populations.
Reasoning: Most amphibian populations naturally fluctuate significantly from year to year due to changes in the weather.
Analysis: The author assumes that the 'natural variations' caused by weather are indistinguishable from the 'dramatic' declines attributed to pollution. To make the argument work, the author needs it to be true that the current decline isn't so massive or unique that it exceeds what weather could reasonably cause. If the current decline were 99% of the population and weather only ever caused a 10% dip, we *could* be fairly sure pollution (or something else) was at play. Look for an answer that bridges the gap by suggesting the recent decline falls within the realm of what natural variation might explain.
Passage Stimulus
Passage Redacted
Unlock Full Passage25.The argument depends on assuming which one of the following?
Correct Answer
A
A is correct because the author’s doubt relies on weather being a live alternative explanation for these specific species. If these species were known to be ones whose populations do not vary with weather, the weather point would not undercut certainty about pollution. Negation test: If the declining species are known to be among those that do not vary greatly due to weather, then pointing to weather variability in “most species” cannot justify “impossible to be sure,” and the argument collapses.
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