Two small and heavy spheres, each of mass M. are placed a distance r apart on a horizontal surface The gravitational potential at the mid-point on the line joining the centre of the spheres is

Q: Two small and heavy spheres, each of mass M. are placed a distance r apart on a horizontal surface The gravitational potential at the mid-point on the line joining the centre of the spheres is

(a) Zero

(b) -GM/r

(c) -2GM/r

(d) (-4GM)/r