【单选题】【消耗次数：1】
随机选取男200人,女100人为某寄生虫病研究的调查对象,测得其感染阳性率分别为20%和15%，则合并阳性率为（ ）
①
35%
②
16.7%
③
18.3%
④
无法计算
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