In a quadrilateral abcd, the diagonals bisect each other at point t. based on the given information which statement is presented first to show that side ab is equal to side bc? a: angle adt is congruent to angle atb. b: angle atb is congruent to angle ctb. c: side bc is equal to the diagonal ac of the quadrilateral. d: side ab is equal to the diagonal db of the quadrilateral.