单选题(共8题,40.0分)-|||-1. () 设x1:x2···xn为来自总体N(1.4)的样本,-|||-元为样本均值,则下列结论中正确的是-|||-A .dfrac (overline {x)-1}(2/sqrt {n)}sim t(n)-|||-B .dfrac (1)(4)sum _(i=1)^n(({x)_(i)-1)}^2sim F(n,1)-|||-C .dfrac (overline {x)-1}(2/sqrt {n)}sim N(0,1)-|||-D .dfrac (1)(4)sum _(i=1)^n(({x)_(i)-1)}^2-(x)^2(n)