Answer:
B. Because they act on different objects. .
Step-by-step explanation:
Newton's third law of motion states that:
"when an object A exerts a force on an object B, then object B exerts an equal and opposite force on object A. These two forces are called action and reaction"
As we see from the description of the law, the action and the reaction do not act on the same object: in fact, the action is exerted on object B, while the reaction is exerted on object A.
In the example of the swimmer, the action is the force that the swimmer exerts on the water, while the reaction is the force that the water exerts on the swimmer: these two forces are not exerted on the same object, so the correct choice is
B. Because they act on different objects.