In which of the following are action and reaction forces involved?
a. when hitting a baseball with a bat
b. walking
c. swimming
d. all of the above

D. All of the above

Explanation:

Newton's third law states that:

"when an object A exerts a force on an object B, object B exerts an equal and opposite force on object A. These forces are called action and reaction"

Let's analyze each situation:

A. when hitting a baseball with a bat --> we have two objects (the baseball and the bat), so we have a pair of forces: the action is the force exerted by the baseball on the bat, while the reaction is the force exerted by the bat on the baseball

B. walking --> in this case, the two objects we should consider are the man walking and the road: the action is the force exerted by the feet of the man on the road, while the reaction is the force exerted by the road on the feet of the man, which allows him walking

C. swimming --> in this case, the two objects we should consider are the man swimming and the water around him: the action is the force exerted by the body of the man on the water, while the reaction is the force exerted by the water on the body of the man, which allows him to swim.

So, all the three choices are correct.