单项选择题
A.整群抽样 B.分层抽样 C.系统抽样 D.单纯随机抽样
A.35% B.45% C.50% D.40%
A.95% B.90% C.98% D.92%
A.轻质 B.绝热 C.耐热性差 D.吸水率小
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