What about these molecules requires them to have this tetrahedron shape?

There are four atoms required for having tetrahedron shape.

Explanation:

Tetrahedron shape molecule is made up of four atoms. The structure of tetrahedron shape molecule is just like pyramid. One atom is present at the top while the remaining three atoms attached to it at the bottom with bond angles of about 109.5°. So the structure of molecules only be possible if the molecule is made up of at least four atoms and have four unpaired electrons. Examples of such molecules are methane, water and ammonia.

b.have there own function.

paper covers rock.

explanation:

rock only smashes scissors.