A child is pushed periodically on a swing at a time interval equal to the swing’s natural period. After several pushes, the person stops pushing and steps away. Which statement best describes the motion of the swing immediately after the pushes stop?
(a) The swing continues with the same large amplitude indefinitely.
(b) The swing oscillates at its natural frequency with gradually decreasing amplitude.
(c) The swing oscillates with a slowly decreasing frequency while its amplitude remains nearly constant.
(d) The swing comes to rest almost immediately after the external pushes stop.