Three concentric metallic spherical shells of radii R, 2R, 3R, are given charges Q, Q2, Q3, respectively. It is found that the surface charge densities on the outer surfaces of the shells are equal. Then, the ratio of the charges given to the shells, Q Q2 : Q3, is (A) 1:2:3 (C) 1:4:9 (B) 1:3:5 (D) 1:8:18