The ruling minimum radius of the curve for ruling design speed V m/sec, coefficient of friction f, acceleration due to gravity g $$m/sec^2$$ and superelevation e is given by

A

$$ \frac {V^2} {(e - f) g} $$

B

$$ \frac {V^2} {(f - e) g} $$

C

$$ \frac {V^2} {(e + f) g} $$

D

$$ \frac {V^2} {(e + f) 2g} $$