Final answer:
The cause of a body in motion to resist any change is its inertia, as per Newton's first law of motion. Inertia is related to the mass of an object, with more massive objects having more inertia. The correct option is A.
Step-by-step explanation:
The cause of a body in motion to resist any change is the body's inertia. Inertia is the property of a body to remain at rest or to continue in motion with constant velocity unless acted upon by a net external force.
This is described by Newton's first law of motion, which is also known as the law of inertia. Inertia is directly related to the mass of an object: objects with greater mass have more inertia and thus resist changes in their motion more than objects with less mass.
Inertia is why it is difficult to push a large boulder but easier to push a basketball. It is not directly related to acceleration, speed, or momentum. These properties are linked to motion, but inertia itself is the tendency to resist change in motion.
Therefore, the correct is A.