In quadrilateral ABCD, diagonals AC and BD bisect one another: Quadrilateral ABCD is shown with diagonals AC and BD intersecting at point P. What statement is used to prove that quadrilateral ABCD is a parallelogram? A. Angles ABC and BCD are congruent. B. Sides AB and BC are congruent. C. Triangles BPA and DPC are congruent. D. Triangles BCP and CDP are congruent.