The Momentum of a System of Particles Is Conserved If

Multiple Choice

The momentum of a system of particles is conserved if

A) there are an even number of particles in the system to allow an integer number of action-reaction pairs.
B) the net force on each particle making up the system is zero.
C) the momentum of each particle making up the system is conserved.
D) no external forces are acting on the system.
E) no internal forces are acting on the system.