设X1,X2,···,Xn是来自正态总体N(μ,σ^2)的简单随机样-|||-本,X是样本均值,记-|||-({S)_(1)}^2=dfrac (1)(n-1)sum _(i=1)^n(({X)_(i)-overline (X))}^2, ({S)_(2)}^2=dfrac (1)(n)sum _(i=1)^n(({X)_(i)-overline (X))}^2,-|||-({S)_(3)}^2=dfrac (1)(n-1)sum _(i=1)^n(({X)_(i)-mu )}^2, ({S)_(4)}^2=dfrac (1)(n)sum _(i=1)^n(({X)_(i)-mu )}^2,-|||-则服从自由度为 n-1 的t分布的随机变量是 () .-|||-(A) =dfrac (overline {X)-mu }({S)_(1)/sqrt (n-1)}; (B) =dfrac (X-mu )({S)_(2)sqrt (n-1)}-|||-(C) =dfrac (overline {X)-mu }({S)_(3)sqrt (n-1)}; (D) =dfrac (X-mu )({S)_(4)sqrt (n-1)}