Consider the function $f(x) = 3-3 x^{2/3}$ on the interval $[ -1 , 1 ]$.

Which of the three hypotheses of Rolle's Theorem fails for this function on the inverval?

(a) $f(x)$ is continuous on $[-1,1]$.
(b) $f(x)$ is differentiable on $(-1,1)$.
(c) $f(-1)=f(1)$.