单项选择题
A.16.8kJ B.17.2kJ C.23.5kJ D.29.3kJ E.39.5kJ
A.25% B.20% C.15% D.12% E.10%以下
A.单纯随机抽样 B.系统抽样 C.整群抽样 D.分层抽样 E.多阶段抽样