Polar moment of inertia of a hollow shaft having D and d as outer and inner diameters, is given by:

A

$$\frac{\pi}{4}(D^{4}-d^{4})$$

B

$$\frac{\pi}{32}(D^{4}-d^{4})$$

C

$$\frac{\pi}{64}(D^{4}-d^{4})$$

D

$$\frac{\pi}{12}(D^{4}-d^{4})$$