20. Let f be a function that is differentiable on the open interval (a,b). If f has a relative
minimum at (c,f(c)) and a I.
f'(c) = 0.
II.
f" (c) must exist.
III.
If f" (c) exists, then f" (c) > 0.
(A) I only
(B) I and II only
(C) I and III only
(D) I, II, and III