20.(5%) Let X1,X2, ....Xn be n identical and independently distributed exponential random variables with fxi(x) = e-xu(x), u(x) = 1 for x ≧ 0,0 otherwise. The maximum value for the probability density function, fzn(z), of the random variable Zn = max(Xi, X2,.... Xn) occurs at z =?
(A) In(n)
(B) In(-1)
(C) In(1/n)
(D) (1 -e-1)n
(E) n(1-e-1)n
答案：99
統計：A:0,B:0,C:0,D:0,E:0
難度：計算中