= Solution
{c}
The <Bravais lattice> is a <face-centered cubic lattice>. Four inequivalent representatives of its <lattice points> in the conventional cubic <unit cell>, in <fractional crystal coordinates>, are
$$
(0,0,0),\qquad\left(0,\frac12,\frac12\right),\qquad
\left(\frac12,0,\frac12\right),\qquad
\left(\frac12,\frac12,0\right).
$$
Boundary copies in the drawing do not constitute additional independent <lattice points>. Attach the two-atom <atomic basis>
$$
\boxed{\mathrm{Al}:(0,0,0),\qquad
\mathrm{P}:\left(\frac14,\frac14,\frac14\right)}
$$
to each <lattice point>. The resulting <aluminium phosphide> <crystal structure> is the <zinc blende structure>. For example, the four <phosphorus> positions reduced into the conventional <unit cell> are $(1/4,1/4,1/4)$, $(1/4,3/4,3/4)$, $(3/4,1/4,3/4)$, and $(3/4,3/4,1/4)$, reproducing the heights in the source drawing. There are four <aluminium> and four <phosphorus> <chemical atoms> per conventional <unit cell>, but only two <chemical atoms> per <primitive unit cell>.
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