25.设正态分布函数,-|||-_(i)= 0,否则 i=1, 2,···,100,-|||-1,事件A发生-|||-且 P(A)=0.3 x1,x2,···,x100相互独立。令 =sum _(i=1)^100(X)_(i), 则由中心极-|||-限定理知Y的分布函数F(y)近似于(B)。-|||-A.ϕ(y) B. (dfrac (y-30)(sqrt {21)}) C. (dfrac (y-30)(21)) D. bigcirc (1)(y-30)