题目15.设X与Y为相互独立的随机变量,则下列结论不正确的是 ()-|||-A. E(X+Y)=E(X)+E(Y) B. D(X+Y)=D(X)+D(Y)-|||-C. E(3X)=3E(X) D. (3x)=3D(x)题目解答答案优质解答