Aperson standing on a horizontal floor is acted upon by two forces: the downward pull of gravity and the upward normal force of the floor. these two forces a. have equal magnitudes and form an action-reaction pair. o b. have equal magnitudes and do not form an ac n pair 0 c. have unequal magnitudes and form an action-reaction pair. 0 d. have unequal magnitudes and do not form an action-reaction pair