According to Newton's law of universal gravitation, if the distance between two point masses increases from $r$ to $2r$ while the masses remain the same, how does the gravitational force change?

• A. It becomes one-half as large: $F^{\prime }=\frac{F}{2}$.
• B. It becomes twice as large: $F^{\prime }=2F$.
• C. It remains the same: $F^{\prime }=F$.
• D. It becomes one-fourth as large: $F^{\prime }=\frac{F}{4}$.

Answer: (D)