There are three co-centric conducting spherical shells $\mathrm{A}, \mathrm{B}$ and $C$ of radii $\mathrm{a}, \mathrm{b}$ and $c$ respectively $(c>b>a)$ and they are charged with charge $q_1, q_2$ and $q_3$ respectively. The potentials of the spheres $\mathrm{A}, \mathrm{B}$ and $C$ respectively, are: