单项选择题
A.13.62% B.16.66% C.15.84% D.15.94%
A.两次均失败 B.第一次成功或第二次失败 C.第一次成功且第二次失败 D.两次均成功
A.0.28,0.21 B.0.5,0.25 C.0.56,0.28 D.0.72,0.36