(4)设(X1,X2,···,X66)是来自总体 approx N(0,(sigma )^2) 的样本,则 () ~-|||-F(2,4).-|||-(A) dfrac (2({{X)_(1)}^2+({X)_(2)}^2)}({{{_{{{r)_(3)}^2+({X)_(4)}^2+({X)_(5)}^2+({X)_(6)}^2} (B) dfrac ({{X)_(1)}^2-({X)_(2)}^2}({{X)_(3)}^2+({X)_(4)}^2+({X)_(5)}^2+({X)_(6)}^2}-|||-(C) dfrac ({{X)_(3)}^2+({X)_(4)}^2+({X)_(5)}^2+({X)_(6)}^2}({{X)_(1)}^2+({X)_(2)}^2} (D) dfrac (2({{X)_(1)}^2+({X)_(2)}^2+({X)_(3)}^2+({X)_(4)}^2)}({{X)_(1)}^2+({X)_(2)}^2}