Hint: The inertia of a body is its nature to resist any change in its current state of rest or uniform motion. Heavy objects are difficult to move than lighter objects because they have more inertia than lighter objects.
Complete step-by-step answer The inertia of a body is the tendency of that body to resist any change. Every particle or body in the universe has the nature to remain in its present state whether it is at rest or travelling in a uniform motion. The body does want any change in its motion (inertia of motion) and it also does want to move from its state of rest (inertia of rest). That is why an external force is needed to be applied to the body to change its present state i.e. to accelerate it. When a force is applied to the body, the magnitude of acceleration depends on the mass of the body. We can also say that the inertia of a body is directly proportional to the mass of the body. Suppose there are two bodies of different masses the same force is applied on both the bodies the body with a larger mass will have less acceleration than the other body. For example, it is very difficult to move a heavy boulder (larger mass) because its mass is very large and the inertia is more. Whereas it is easy to move a lighter stone because it has very less mass and thus less inertia. Therefore, it cannot resist to that extent and moves very easily.
Hence the correct answer to the above question is (A) Mass of the body.
Note The mass and the inertia of a body are not the same but related to each other. A light body with a large magnitude of velocity, acceleration, and energy can be easily brought to rest or its direction of motion can easily be changed hence options (B), (C) and (D) are incorrect.