The statement that best provides evidence that a scientific law is a description while a scientific theory is an explanation is:
"Laws of motion state that for any action force, there is an equal and opposite reaction force, while theories state that contact forces are due to electrostatic forces between the charged particles that make up matter."
This statement clearly illustrates the difference: the law describes a consistent observation (the action-reaction principle), while the theory provides an explanation for the underlying mechanisms (electrostatic forces).