Two uniform spheres with equal mass per unit volume are in contact with one another. The mass of sphere A is five times that of sphere B. 

The center of mass of the system is
(a) At the point where A and B touch.
(b) Inside sphere B somewhere on the line joining the centers of A and B.
(c) Inside sphere A somewhere on the line joining the centers.
(d) At the center of sphere A.
(e) Outside of both spheres.