At the moment there are 54,210 tagged birds in a certain wildlife refuge. If exactly 20 percent of all birds in the refuge are tagged, what percent of the untagged birds must be tagged so that half of all birds in the refuge are tagged?
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A25
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B30
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C$$33\frac{1}{3}$$
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D$$37\frac{1}{2}$$
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E50
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正确答案: D