A pendulum consists of a heavy but very small bob of mass $$M$$ suspended at the end of a rigid rod of mass $$m$$ and length $$L$$. The time period of small oscillations in the vertical plane, about a horizontal axis through the upper end of the rod is

A

$$2\pi\sqrt{\frac{m + 2M}{m + 3M}\frac{3L}{2g}}$$

B

$$2\pi\sqrt{\frac{m + 3M}{m + 2M}\frac{2L}{3g}}$$

C

$$2\pi\sqrt{\frac{3L}{2g}}$$

D

$$2\pi\sqrt{\frac{2m + M}{3m + M}\frac{3L}{2g}}$$