A force between two objects comes into play when
A) both objects are very heavy.
B) both objects move with some speed.
C) the objects interact with each other.
D) All of the above.

Hint: In science, a push or a pull is referred to as a force. A force is said to exist between two objects when one object pushes or pulls the other object and thereby changes the state of the object. A force must cause some acceleration in the object.

Complete step by step answer:
The force acting on the two objects can be described by a physical example.
Force can be vaguely described as a push or a pull. This suggests that at least two objects must be present for a force to exist. Object 1 can be pushing or pulling the object 2 and vice-versa.
Consider the case when a person pushes a table for some distance across the room. Here, the person is essentially applying a force on the table which results in the motion of the table.
Now consider the case when a person catches a ball in the air. Here the person exerts a force to stop the motion of the ball.
In both these situations, the action of the person caused a change of state. For the table, its state changed from being at rest to being in motion while for the ball, its state changed from being in motion to being at rest. So we conclude that the interaction of the person with the object (table or ball) resulted in a force.

Thus when two objects interact with each other force exists. So the correct option is C.

Note:
The table was initially at rest and so it did not have any speed. The ball is not a very heavy object but it came to a rest when the person caught it. In the above two scenarios, we see that the heaviness of the object and its speed does not matter for a force to exist. But the amount of force required to move the table or to catch the ball will depend on the mass and the change in velocity of the two objects.