Hygiene investigation was carried out in 156 classrooms of 36 schools with stratification sampling.

采用分层抽样方法，对36所学校、156间教室进行卫生学调查。

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Hygiene investigation was carried out in 156 classrooms of 36 schools with stratification sampling.

采用分层抽样方法，对36所学校、156间教室进行卫生学调查。

youdao