18. Suppose Y is a Poisson random variable with mean A - 4 and X is a Chi-square random variable with degree of freedom df = 2. Which of the following statement is the most correct one?
(A) Covariance between X and Y is greater than 6；
(B)E[X +Y] = 4；
(C)Variance of X+ Y equals to 8；
(D)Covariance between 2X and 3Y is between -24 and 24；
(E)Variance of X + Y is between 8 and 16.
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