设X1,X2,···, _(n)(ngeqslant 2) 为来自总体N(μ,1)的简单随机样本,-|||-记 overline (x)=dfrac (1)(n)sum _(i=1)^n(x)_(i), 则下列结论正确的是 ()-|||-(A) sum _(i=1)^n(({X)_(i)-mu )}^2 服从x^2分布-|||-(B) (({X)_(n)-(X)_(1))}^2 服从x^2分布-|||-(C) sum _(i=1)^n(({X)_(i)-overline (X))}^2 服从x^2分布-|||-(D) ((overline {x)-mu )}^2 服从x^2分布