Answer:
D. the force of gravity on a falling ball
Step-by-step explanation:
A non-contact force is a force that is applied to an object by another object without contact. Gravity, electrostatic force, and magnetic force all don't need two objects to be touching in order for them to work.
On the other hand, an example of a contact force is friction, because it can only occur if two objects are touching. If you want to tell the difference between a contact and non-contact force, just ask yourself if it can occur if the two objects are not touching. If it can occur while two objects aren't touching, it is non-contact, and if it can't, it is contact.
