4、5个灯泡的寿命x1,x2,x3,x4,x3轴立同分布且-|||-(X,)=a, (x,)=b, (i=1,2,3,4,5), 则5个灯泡的平均寿命-|||-=dfrac (1)(5)((X)_(1)+(X)_(2)+(X)_(3)+(X)_(4)+(X)_(5)) 的方差 (n)= ()-|||-A、5b: B、b; C、0.2b; D、0.04b.