Answer: Option d
Step-by-step explanation:
According to Newton's third law, for every force "P" that is applied on an object there is a force -P that has the same maginitud that "P" and opposite direction.
In other words "for every action there is an equal and opposite reaction"
For example, if Object D applies a force "P" on an object B, then object B will make a force -P on object D.
This force is called the reaction force.
Therefore when the swimmer pushes the wall, then the wall pushes the swimmer with a force of the same magnitude that is called the reaction force.