Which of the following statements is/are true? (5 points)
I.If f '(x) exists and is nonzero for all x, then f(1) ≠ f(0)
II.If f is differentiable for all x and f (-1) = f(1), then there is a number c, such that |c| < 1 and f '(c) = 0.
III.If f '(c) = 0, then f has a local maximum or minimum at x = c.



I only
II only
I and III only
I and II only