There are three co-centric conducting spherical shells \( A, B \) and \( C \) of radii \( a, b \) 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 \( A, B \) and \( C \) respectively, are: