A certain crystal, $X$, is formed from two types of atom, $A$ and $B$. The atoms of $A$ are found at all the points, and only the points, with coordinates $(l, m, n)$ for any whole numbers $l, m, n$; the atoms of $B$ are found at all the points, and only the points, with coordinates $(l+0.5, m+0.5, n+0.5)$.
Think about the geometry of this crystal. Can you visualise its structure? Can you devise a clear pictorial representation? How simply can you describe its structure in words?
How close are the various $A$ and $B$ atoms to each other? What bond angles are formed?
What crystal structure does this represent?
Can you represent any other crystal structures in a similar way?