Simplify $$\frac{(r-s)^{3}+(s-t)^{3}+(t-r)^{3}}{6(r-s)(s-t)(t-r)}$$

A

$$\frac{1}{6}$$

B

$$\frac{1}{2}$$

C

$$\frac{1}{3}$$

D

$$\frac{1}{4}$$