Newton's 2nd Law states An object acted on by an unbalanced force will accelerate in the direction of that
force, in direct proportion to the strength of the force, and in inverse proportion
to the mass of the object.
For every action there is an equal and opposite reaction
Objects in motion will stay in motion; objects at rest will stay at rest unless an
unbalanced force is applied.

Answertraveling around a circular trackexplanation"traveling around a circular track" is the best answer as you could be traveling around a circular track at a constant speed. your velocity would therefore have the same magnitude but will always be constantly direction. since acceleration is the rate of change of velocity, the rate of change will only involve the direction of velocity and not the magnitude.wrong choices: "an object at rest" does not accelerate at all"increasing speed while traveling around a curve" means that the acceleration will not be constant due to only change in direction; it will be constant due to both magnitude and direction"an object in free fall" does not necessarily change direction 

Ithink the answer is d