For every action force, there must be a reaction force that a. always act simultaneously. b. acts in the opposite direction c. is equal in magnitude. d. all of the above

The correct answer is **d. all of the above**. According to Newton's Third Law of Motion, for every action force, there is an equal and opposite reaction force. This means that: a. The action and reaction forces do indeed act simultaneously. b. They act in opposite directions. c. They are equal in magnitude. So, all the statements are true.