If D is the diameter of Pelton wheel and d is the diameter of the jet, then number of buckets on the periphery of a Pelton wheel is equal to

A

$$\frac{D}{2d}$$

B

$$\frac{D}{2d} + 10$$

C

$$\frac{D}{2d} + 15$$

D

$$\frac{D}{2d} + 20$$