Methods: Chester sampling of the children aged 3 to 6 in four local kindergartens in Shaoguan City, Guandong Province, was carried out.
方法：整群抽取广东省韶关市区四所幼儿园的3 ~6岁儿童作为调查对象。
Methods: Chester sampling of the children aged 3 to 6 in four local kindergartens in Shaoguan City, Guandong Province, was carried out.
方法：整群抽取广东省韶关市区四所幼儿园的3 ~6岁儿童作为调查对象。
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