10.设X1,X2,···,Xn为来自总体X的样本, dfrac ( )(1) 为样本均值,则样本方差 ^2= .()-|||-A.1/n (x1-x^2)^2 B. dfrac (1)(n-1)sum _(i=1)^n(({X)_(i)-overline (X))}^2 .-|||-n-|||-C. sqrt (dfrac {1)(n)sum _(i=1)^n(({X)_(i)-overline (X))}^2} . D. sqrt (dfrac {1)(n-1)}sum _(i=1)^n(({X)_(i)-overline (X))}^2