Pyramid
Triangle
A tetrahedron = triangle based pyramid.
By its very nature of being a triangle, and a 2D shape, a triangle cannot have four plane faces. However, a tetrahedron is a polyhedron made up of four triangular faces.
A tetrahedron is the smallest possible polyhedron: a closed 3-d shape with polygonal faces. It has 4 triangular faces, 4 vertices and 6 edges. It is also known as a triangle-based pyramid.
Regular Tetrahedron
four triangle faces.
tetrahedron
A pyramid has a variable number of triangular faces. The base of a triangle can be practically any regular shape, starting with a triangle. Technically a pyramid can have four or more triangles as faces.
The answer is a polyhedron
a pyramid
A pyramid.
triangle... because pyramids are triangular therefore triangular pyramids have triangle faces