12.)
What is a tetrahedron? Now construct a tetrahedron.

A
regular tetrahedron, referred to as "the" tetrahedron, is
a Platonic solid, regular solids and polyhedra that are convex with
equivalent faces made of congruent convex regular polygons, that contains
four polyhedron vertices, six polyhedron edges, and four equilateral
triangular faces. Tetrahedra are considered uniform polyhedra, polyhedra
with identical polyhedron vertices, a Wenninger model, and is described
by the Schläfli symbol {3,3} and the Wythoff symbol 3|23. This
has seven axes of symmetry. This is also the ONLY convex polyhedron
that has four faces.

This
information was found at http://mathworld.wolfram.com/Tetrahedron.html