单项选择题
A.50/450×100/100=11.11% B.200/450×100/100=44.44% C.450/500×100/100=90% D.400/550×100/100=81.82% E.450/650×100/100=53.85%
A.300/350×100/100=85.71% B.200/450×100/100=44.44% C.450/500×100/100=90% D.200/500×100/100=40% E.300/500×100/100=60%
A.分层抽样 B.系统抽样 C.整群抽样 D.单纯随机抽样 E.普查