Correct Response: C. Mass is both a measure of the quantity of matter in an object and a measure of an object's resistance to changing its state of motion when acted upon by an outside force. Therefore, the inertia of an object varies directly with the object's mass. A is incorrect because weight, while often incorrectly used interchangeably with mass, is the force created when a mass is acted upon by gravity. Momentum (B) is the product of mass and velocity and is not directly related to inertia. Acceleration (D) is the rate of an object's change in velocity over time and is also not directly related to inertia.