儿童龋齿患病率的高低与饮水中含氟量有关,当饮水中含氟量在0.5PPm以下, 人群中龋齿患病率明显上升,这种逻辑法是( )
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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