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某地区进行学龄儿童流脑疫苗接种率调查，首先将该地区分为好中差三类，然后在每类中随机抽1/10的学龄儿童进行调查，这种抽样方法属于（）
A . 多级抽样
B . 系统抽样
C . 分层抽样
D . 整群抽样
E . 单纯随机抽样
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