Inertia is the resistance of an object to changes in its motion, which increases as mass increases. Hence, if an object's mass increases, its inertia also increases. The correct answer is that inertia increases. ;
Inertia is the resistance of an object to changes in its motion, and it is directly related to mass. As an object's mass increases, its inertia also increases. Thus, the correct answer is option C: It increases.
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