複選題

十六. Consider the famous hat problem as in the previous problem. Let X, be a random variable that takes value 1 if the ith person selects his/her own hat, and takes value O otherwise. Let cov(Y, Z) = [Y . Z] -E[Y] ㆍE[Z] be the covariance of two random variables Y and 2. Which of the following statements is/are true?
(A) When n = 4, cov(X₄, X₄) is .
(B)When n = 4,cov(X₁,X₂)=
(C) When n = 4, va=2.
(D) When n = 4, Xi and Xz are statistically independent.
(E) For any two random variables Y and Z, cov(Y, Z) ≥0.