设总体 sim N((M)_(2)(O)^2) ,(X1,X2,···Xn)为来自总体X的简单随机样本,则下列-|||-结论不正确的是 ()-|||-A .(overline (X))=mu ;-|||-B (overline (X))=dfrac ({sigma )^2}(n) ;-|||-C overline (X)sim N((mu )_(1)(sigma )^2)-|||-D .overline (X)sim N(mu ,dfrac ({sigma )^2}(n)) 4