The ancient Pythagoreans studied figurate numbers, which are numbers that can be shown by taking dots or spheres and arranging them into geometric shapes. For example, the square numbers are 1, 4, 9, 16, 25, etc., and each of these numbers of dots can be arranged into a square. The tetrahedral numbers similarly specify the number of spheres needed to create a tetrahedron, which is a triangular-based pyramid. The tetrahedral numbers are 1, 4, 10, 20, 35, 56, 84, etc. Which of the following statements is true? A B C D The tetrahedral numbers are best modeled by a quadratic function because the 2nd differences are a nonzero constant. The tetrahedral numbers are best modeled by a quadratic function because the 3rd differences are a nonzero constant. The tetrahedral numbers are best modeled by a cubic function because the 2nd differences are a nonzero constant. The tetrahedral numbers are best modeled by a cubic function because the 3rd differences are a nonzero constant.