A straight line.
A tetrahedron.
A triangular prism can have a square or triangular base.
the base of a triangular pyramid is triangle
the base of a triangular pyramid is triangle
a square * * * * * That would be a square pyramid! A triangular pyramid would have ... wait for it ... a TRIANGULAR base! Worth waiting for, wasn't it?
Triangular Pyrimid
A triangular prism can have a square or triangular base, but faces are normally triangles. (I think)
A pyramid.
That would be a triangular pyramid.
A pyramid with an irregular pentagon base.
It is a pyramid
It is normally rectangular in shape.