Answer:
A. Mass
Step-by-step explanation:
Inertia is the resistance of an object to any change in its velocity. Inertia depends only on the mass of the object: the greater the mass, the larger the inertia of the object, because it will be more difficult to change the velocity of the object.
An example to better understand: assume there is a golf ball rolling with a certain speed, and a car moving with the same speed. If we want to stop the two objects, we will need a much larger force for the car, because its mass is much greater than the gold ball, so it has much more inertia than the golf ball.