The force of attraction between two objects of masses 'M' and 'm' which lie at a distance 'd' from each other is directly proportional to the-

A

Difference between masses of objects $$M - m$$

B

Sum of the masses of objects $$M + m$$

C

Product of the masses of objects $$M \times m$$

D

Sum of the squares of masses of objects $$M^2 + m^2$$