5.设X1,X2,X3是来自总体X的简单随机样本,且 (X)=mu , 则下列统计量不是μ的无偏估计量-|||-的是-|||-(A) dfrac (1)(3)((X)_(1)+(X)_(2)+(X)_(3)). (B) dfrac (2)(3)(X)_(1)+dfrac (1)(3)(X)_(2) (C) _(1)+(X)_(2)+(X)_(3) (D) dfrac (1)(4)((X)_(1)+(X)_(2))+dfrac (1)(2)(X)_(3)-|||-二、填空题:每小题2分,共10分,