Mechanical equilibrium: Select one: A. Defines systems in terms of force and this is the only way to analyse mechanical equilibrium. B. Can be found in a system that has velocity if the velocity is equal to a varying quantity. C. There are situations of rotational mechanical equilibrium, and in these, the angular momentum of the object is conserved and the net torque may be a moveable quantity. D. May be expressed in terms of momentum, a system is in equilibrium if the momentum of its parts is equal to a mutable quantity. E. None of the above