Two planets revolve round the sun with frequencies `N_(1)` and `N_(2)` revolutions per year. If their average orbital radii be `R_(1)` and `R_(2)` respectively, then `R_(1)//R_(2)` is equal to
A. `(N_(1)//N_(2))^(3//2)`
B. `(N_(2)//N_(1))^(3//2)`
C. `(N_(1)//N_(2))^(2//3)`
D. `(N_(2)//N_(1))^(2//3)`
