Three concentric metallic spherical shells of radii R, 2R, 3R are given charges `Q_(1) Q_(2) Q_(3)`, respectively. It is found that the surface charge densities on the outer surface of the shells are equal. Then, the ratio of the charges given to the shells `Q_(1) : Q_(2) : Q_(3)` is
A. `1 : 2 : 3`
B. `1 : 3 : 5`
C. `1 : 4 : 9`
D. `1 : 8 : 18`
