10)设总体x服从正态分布N(10,3^2),X1,X2,···,X6-|||-是它的一组样本,设 overline (X)=dfrac (1)(6)sum _(i=1)^6X 则X所服从的分布-|||-为 () .-|||-A overline (X)sim N(7,1)-|||-B overline (X)sim N(5,dfrac (3)(2))-|||-C overline (X)sim N(10,dfrac (3)(2))-|||-D overline (X)sim N(10,dfrac (1)(2))