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 a three-dimensional geometric shape with four triangular faces, six edges, and four vertices. Its shape resembles a pyramid, where each of the four faces is an equilateral triangle.
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
Triangle
A pyramid.