Concept:A triangular prism is a 3D shape with two triangular bases and three rectangular side faces.Explanation:Count the edges on the two triangular bases.Each triangular base has 3 edges.So both bases together give 3+3=6 edges.Now count the edges joining the two bases along the side faces.There are 3 lateral edges connecting corresponding vertices.Total edges =6+3=9.Therefore, a triangular prism has 9 edges.Answer:D. 9