Gravity is universal; all objects attract each other with a force and the magnitude of that attraction force is, in part, depicted in this model. what assumption is made by the model regarding the force of gravitational attraction.

a) the gravitational force is directly proportional to the mass of both interacting objects.
b) if the distance between two objects doubles, the force of attraction between the objects is cut in half.
c) as the mass of either object increases, the force of gravitational attraction between them also increases.
d) as the distance between two objects increases, the force of gravitational attraction between them decreases.