Step 1: Concept
Newton's Law of Universal Gravitation states that the gravitational force is $F = G M m / r^2$.
Step 2: Meaning
Acceleration ($a$) is defined as Force divided by mass ($F/m$).
Step 3: Analysis
Dividing the gravitational force equation by the mass of the body ($m$), we get $a = GM/r^2$. Since $G$ and $M$ (mass of Earth) are constants, $a \propto 1/r^2$.
Step 4: Conclusion
The acceleration is inversely proportional to the square of the distance from the center of the Earth.
Final Answer: (C)