4.3. Let X be Na(u, E) with u' = [-3, 1, 4] and 1 -2 0 - E = -2 5 0 0 0 2 Which of the following random variables are independent? Explain. (a) X, and X2 (b) X2 and X3 (c) (X1, X2) and X3 (d) X1 + X2 2 and X3 (e) X2 and X2 - 3X1 - X3