【单选题】
某企业连续生产其产品，为了检查产品的质量，在20小时内每隔30分钟取出下一分钟的产品进行全部检查，这种方法是（ ）。
①
简单随机抽样
②
整群抽样
③
类型抽样
④
等距抽样
【单选题】
某债券的面值为1000元，，票面年利率为12%，期限为3年。若市场年利率为10%，则其发行价格（ ）
①
大于1000元
②
小于1000元
③
等于1000元
④
无法计算
【单选题】
A点坐标为（10、20、30），B点坐标为（30、20、30）则AB距离为______。
①
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