If XXX and YYY are independent, which is always true?
Cov(X,Y)=0Cov(X, Y) = 0Cov(X,Y)=0
Var(X+Y)=Var(X)+Var(Y)Var(X + Y) = Var(X) + Var(Y)Var(X+Y)=Var(X)+Var(Y)
E[XY]=E[X]E[Y]E[XY] = E[X]E[Y]E[XY]=E[X]E[Y]
All of the above