单项选择题
A.12个月 B.15个月 C.18个月 D.20个月 E.24个月
A.90/60 B.80/50 C.80/60 D.90/50 E.90/55
A.1:3 B.1:3~1:4 C.1:4 D.1:5 E.1:6