Although beavers can still be found throughout the western United States, their number has declined compared with the eighteenth century, when the abundance of beavers lured armies of European trappers into the Rocky Mountain region to slaughter them for their pelts.
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Atheir number has declined compared with
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Btheir numbers have declined compared with
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Ctheir numbers have declined since
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Dtheir numbers have declined in comparison to those of
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Ethe number of them declined since
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