The MA(1 ) process, y. = a + 8, +be .. ~WN N(0.o ) is a covariance stationary process A. for any finite values of b and a B. only when | b ( 1 C. only when | b (> 1 D. only when | b |= 1 F. only when | a > I and | b . I Select one: B. C. D. E