If L is the length of a rail and R is the radius of a curve, the versine h for the curve is _____

A

a=$$\frac{L}{4R}$$

B

a=$$\frac{L_{2}}{4R}$$

C

a=$$\frac{L_{2}}{8R}$$

D

a=$$\frac{L_{2}}{16R}$$