A solid cylinder of mass $M$ and radius $R$ rotates about its axis with angular speed $\omega$. Its rotational kinetic energy is
(a) $\frac{1}{2} M R^{2} \omega^{2}$
(b) $M R^{2} \omega^{2}$
(c) $\frac{1}{4} M R^{2} \omega^{2}$
(d) $\frac{1}{8} M R^{2} \omega^{2}$