有6个一元面值硬币正面朝上放在桌子上,你可以每次翻转5个硬币(必须翻转5个),问你最少经过几次翻转可以使这6个硬币全部反面朝上?( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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