Answer:
A. you push up on a barbell, and the barbell pushes you down
Step-by-step explanation:
As per Newton's third law of motion, every action has an equal and opposite reaction. The point of action and reactionary force are same. If you analyze the options given only first option fulfills this condition.
As you push the barbell up, that means action is being done on the barbell using your hand and barbell pushes you down which means that the reaction force is acting on the same point.
In other options the action is done on one object and the other force is not acting on the same object but some other object.