设计：整群抽样与单纯随机抽样。
DESIGN: a cluster sampling and simple randomized sampling survey.
方法监测点的选择采用单纯随机抽样方法。
Methods Simple random sampling was used to choose surveillance counties.
方法：采用单纯随机抽样方法，对500名农民进行入户问卷调查。
Methods: Using the pure random sampling method, carries on the residence questionnaire survey to 500 farmers.
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