What force determines the motions of planets and other objects in the solar system? A. Static electricity B. Centrifugal force C. The magnetic force D. The force of gravity

The force of gravity

Explanation:

Force of gravity is the force which attracts two masses towards each other.

This force is directly proportional to masses of body and inversely proportional to the square of distance between masses.  

when bodies revolve around the sun, it is attracted by the sun and moves in elliptical path with sun in its center. The axial distance of planet from sun is such that the planet and sun's gravitational force of attraction are equilibrium with each other.