Suppose that f is an odd function; i.e., f(-x)=-f(x) for all x. Suppose that f'(xo) exists. Which of the following must necessarily be equal to f'(-xo)? Select one:
a. - f'(xₒ)
b. f'(xₒ)
c. 1 / f'(xₒ)
d. -1 / f'(xₒ)