A passage discusses how migratory birds navigate using the Earth's magnetic field, the position of stars, and landmarks. The author also notes that light pollution from cities disrupts these navigation methods. What is the primary purpose?
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A
To argue that all cities should turn off their lights at night
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B
To explain how migratory birds navigate and how human activity interferes with this ability
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C
To describe the beauty of bird migration
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D
To compare different bird species