一、选择题-|||-1.设随机变量X和Y都服从标准正态分布,则 ()-|||-(A) +y 服从正态分布 (B) ^2+(y)^2 服从x^2分布-|||-(C)X^2和Y^2都服从x^2分布 (D) ^2/(y)^2 服从F分布-|||-2.设X1,X2,··· _(n)(ngeqslant 2) 为来自总体N(0,1)的简单随机样本,X为样本均值,S^2 ^2为样本方-|||-差,则 ()-|||-(A) overline (X)approx N(0,1) (B) (S)^2approx (x)^2(n)-|||-(C) dfrac ((n-1)overline {x)}(s)approx t(n-1) (D) dfrac ((n-1){{X)_(1)}^2}(sum _{i=1)^n({X)_(i)}^2}approx F(1,n-1)-|||-3.设总体X服从正态分布N(0,σ^2 )(0^2已知),X 1,···,Xn是取自总体X的简单随机样本,S^2-|||-为样本方差,则 ()-|||-A) sum _(i=1)^n({X)_(i)}^2approx (chi )^2(n) (B) ((dfrac {{X)_(i)}(q))}^2+dfrac ((n-1){S)^2}({sigma )^2}approx (chi )^2(n)-|||-(C) dfrac (1)(n)sum _(i=1)^n((dfrac {{X)_(i)}(q))}^2+dfrac ((n-1){S)^2}({sigma )^2}approx (chi )^2(n) (D)1/( (2/3 (x1)/2+(n-1)/2 )S^2 ~x^2(n)-|||-≌(x/a)^2+((x-1)/2~x^2(n)-|||-4.设总体X服从正态分布N(μ1,σ^2 ),总体Y服从正态分布N(μ2,σ^2 ),X1,X2,···,,,,nn,11-|||-Y2,···,Yn,分别是来自总体X和Y的简单随机样本,则-|||-等于 ()-|||-(A) ((n)_(1)+(n)_(2)-2)(sigma )^2 (B) ({n)_(1)(0)^2}+({n)_(2)(sigma )^2}-|||-(C) o^2 (D) dfrac ({sigma )^2}({n)_(1)+(n)_(2)-2}