Let f be differentiable on [0,6] with f(0)=2, f(3)=8, and f(6)=2. Which of the following must be true?
a) There exists e in (3,6) such that f′(e)=2.
b) There exists c in (0,3) such that f′(c)=1.
c) There exists d in (0,6) such that f′(d)=0.
d) f′(x)<0 for all x in (3,6).