Define the principle of conservation of linear momentum and deduce the law of conservation of linear momentum from it.
a) Momentum is conserved when the net external force acting on a system is zero.
b) Momentum is conserved when the net internal force acting on a system is zero.
c) Momentum is conserved when the net external force acting on a system is not zero.
d) Momentum is conserved when the net internal force acting on a system is not zero.