Possibly a face - or an edge. It would help if the question was properly phrased.
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sphere
triangle * * * * * A triangle is NOT a 3d shape! A cube.
The side and face of a 3-D shape are the same thing, but the side of a 3-D object is not, itself 3-Dimensional.
There can be no closed 3D shape with only one square and 3 triangles.
cone