Which of the following is equal to the rational expression when x ≠ 5 or -1
a. (x - 1)(x + 1) / (x - 5)
b. (x - 1)(x + 1) / (x + 5)
c. (x - 5)(x + 1) / (x + 1)
d. (x - 5)(x + 1) / (x - 1)