19. newton’s third law refers to "action-reaction forces". these forces always occur in pairs and a. sometimes act on the same object b. always act on the same object c. may be at right angles d. never act on the same object e. always act at right angles

D. never act on the same object                  

Explanation:

Newton's third law states that for every force applied on an object there is an equal force in magnitude but in the opposite direction. These force come sin pairs called the action reaction forces. When one object applies a force on a second object in one direction, the second object also offers an equal force to the first object in the opposite direction. This is action-reaction force. These two forces occurs on the different objects that forms the action reaction pair of forces.

Hence the correct option is (D).