Which of the following statements is/are true?
A. The total mechanical energy of a system, at any one instant, is either all kinetic or all potential energy.
B. The total mechanical energy of a system is equally divided between kinetic and potential energy.
C. Mechanical energy can be dissipated to nonmechanical forms of energy.
D. The total mechanical energy of a system is constant only if conservative forces act.
E. The total mechanical energy of a system is constant only if nonconservative forces act.