Answer:
d) The trampoline pushes back up on the gymnast.
Step-by-step explanation:
According to Newton's third law of motion; for every action force, there is an equal and opposite reaction force. The action force and reaction force are reciprocal to one another i.e. they act oppositely to one another. The reaction force acts in an opposite direction to the action force and vice versa.
In this question, a gymnast pushed down on a trampoline during a routine. This is called the ACTION FORCE. In conformity to Newton's third law, the trampoline pushes back up on the gymnast. This opposite force is called the REACTION FORCE.