Two marbles are pressed together with a light ideal spring between them, but they are not attached to the spring in any way. They are then released on a frictionless horizontal table and soon move free of the spring. As the marbles are moving away from each other, which of these statements about them are true?

(a) Only the momentum of the marbles is conserved,

(b) Only the mechanical energy of the marbles is conserved,

(c) Both the momentum and the mechanical energy of the marbles are conserved,

(d) The kinetic energy of the marbles is conserved.