Which of the Following Expresses a Principle,which Was Initially Stated

Which of the following expresses a principle,which was initially stated by Galileo and was later incorporated into Newton's laws of motion?

A) An object's acceleration is inversely proportional to its mass.
B) For every action there is an equal but opposite reaction.
C) The natural condition for a moving object is to remain in motion.
D) The natural condition for a moving object is to come to rest.