What happens to the gravitational force if the distance between objects is tripled?

Question

$\begin{array}{1 1} (a)\; \text{The gravitational force becomes $\frac{1}{3}^{rd}$ of its original force} \\ (b)\; \text{The gravitational force becomes $\frac{1}{9}^{th}$ the original force} \\ (c)\; \text{The gravitational is the same as the original force} \\ (d)\; \text{The gravitational force becomes 9 times that of the original force} \end{array}$