Beavers were once trapped nearly to extinction across much of the continent, and the streams they had shaped changed with them. Without dams, water that used to spread slowly across wet meadows now runs straight down cut channels, carrying soil with it and dropping the water table on either bank. Where beavers have returned, the ponds behind their dams hold water through the dry season, and the meadows come back. Some water agencies that once removed the animals as pests now pay to reintroduce them, having calculated what it would cost to build and maintain the same storage in concrete.
The final sentence rests on which unstated assumption?
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Correct answer to question 12 (Paragraph Comprehension): Beaver ponds and engineered reservoirs serve a comparable purpose
Method
The agencies compare the cost of concrete storage with the cost of reintroducing beavers. That comparison only makes sense if the two options do a similar job, which the passage never says outright. The cost of concrete may or may not have risen; the argument does not depend on it.
Updated: November 2026
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