There are 800 runners in a marathon（马拉松）. The mean（平均的）running time is 4 hours exactly. Which of the following must be true?
A: Half the runners take more than four hours.
B: Most people take four hours.
C: The total time taken is 3,200 hours.
D: Everyone takes four hours.
A: Half the runners take more than four hours.
B: Most people take four hours.
C: The total time taken is 3,200 hours.
D: Everyone takes four hours.
举一反三
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