已知一总体 ^Tapprox N((H)_(1)(O)^2), X1,X2,···,Xn是-|||-来自总体的一组样本,样本均值和方差分别为-|||-overline (X)=dfrac (1)(n)sum _(i=1)^n(X)_(i) ^2=dfrac (1)(n-1)(sum )_(i=1)^n((X)_(i)-|||--overline (X)) 则下列结论不正确的是:-|||-A.μ的矩估计和极大似然估计量都是x-|||-B.S是σ的无偏估计量-|||-C.S^2是σ^2的相合估计量-|||-D.X是μ的无偏估计量