Spheres of unit diameter are centered at $(l, m, n)$ where $l, m$, and $n$ take every possible integer values.
The distance between two spheres is computed from the center of one sphere to the center of the other sphere. For a given sphere, $x$ is the distance to its nearest sphere and $y$ is the distance to its next nearest sphere. The value of $\frac{y}{x}$ is:
- $2 \sqrt{2}$
- $\frac{1}{\sqrt{2}}$
- $\sqrt{2}$
- $2$
