What is Newton's first law of motion?

A. For every force there is an equal and opposite reaction force.
B. If a net force is applied to an object, then the object will accelerate.
C. An object will remain at rest or continue moving in a straight line with a constant speed unless acted on by an unbalanced force.
D. The gravitational force between two objects is proportional to their masses and inversely proportional to the distance between them.