If the Angular Momentum of a System Is Constant,which of the Following

Multiple Choice

If the angular momentum of a system is constant,which of the following statements must be true?

A) No torque acts on any part of the system.
B) A constant torque acts on each part of the system.
C) Zero net torque acts on each part of the system.
D) A constant external torque acts on the system.
E) Zero net torque acts on the system.