Newton's 1st law states that:

Newton's 1st law, often referred to as the law of inertia, describes the behavior of objects when no net force is acting upon them. The law states that a body at rest will remain at rest, and a body in motion will continue to move at a constant velocity in a straight line, as long as no external forces are applied. This means that both the first part of the law—about an object remaining at rest—and the second part—which states that an object in motion will keep moving in the same manner—are true.

Combining these two concepts illustrates the law’s comprehensive nature in describing motion. Thus, acknowledging both aspects as correct reflects an understanding of the law as a whole. This is why the answer includes both statements about a body at rest and a body in motion, affirming that both A and C accurately express Newton's 1st law.