Suppose that f is a polynomial function. Which of the following statements is true?
I. If f is increasing at x = a, then f'(a) > 0.
II. If f'(a) > 0, then f is increasing at x = a.
III. If f is decreasing at x = a, then f'(a) < 0.
A. I only
B. II only
C. I and II only
D. I and III only
E. I, II, and III