Which of the following statements is true concerning the elastic collision of two objects?
(a) No work is done on any of the two objects, since there is no external force.
(b) The work done by the first object on the second is equal to the work done on the second by the first.
(c) The work done by the first object on the second is exactly the opposite of the work done on the second by the first.
(d) The work done on the system depends on the angle of collision.