31. A uniform solid ball with mass M is supported by a massless rod. Derive the period of the pendulum with a small displacement.
(A) T = 2π(1.1L/g)1/2
(B) T = 2π(1.8L/g)1/2
(C) T = 2π(1.5L/g)1/2
(D) T = 2π(0.9L/g)1/2
(E) T = 2π(0.7L/g)1/2