Phobus, one of the satellites of Mars, revolves about Mars at a distance of approximately 5,800 miles from the center of Mars and approximately 3,700 miles from the surface of Mars. If it is assumed that Mars is spherical and the orbit of Phobus is circular, what is the approximate circumference, in miles, of Mars at its equator?
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A2,100π
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B4,200π
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C7,400π
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D9,500π
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E190,000π
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正确答案: B