The derivative of a function f(x) defined on (-infinity, infinity) is f'(x) = x³ - 9x, then which of the following statements is true?
(a) The function f(x) has a local maximum at x = 0.
(b) The function f(x) has an absolute minimum at x = 0.
(c) The function f(x) has a local maximum at x = 3 and x = -3.
(d) The function f(x) has an absolute maximum at x = 3 and x = -3.
(e) None of the above.