In a conical pendulum, a bob moves in a horizontal circle, as shown in the figure. The period of the pendulum (the time it takes for the bob to perform a complete revolution) is
a) $T=2 \pi \sqrt{L \cos \theta / g}$.
b) $T=2 \pi \sqrt{g \cos \theta / L}$.
c) $T=2 \pi \sqrt{L g \sin \theta}$.
d) $T=2 \pi \sqrt{L \sin \theta / g}$.
e) $T=2 \pi \sqrt{L / g}$.