In quadrilateral , is congruent to , and is parallel to . Andre has written a proof to show that is a parallelogram. Fill in the blanks to complete the proof.
Since is parallel to , alternate interior angles and are congruent. is congruent to since segments are congruent to themselves. Along with the given information that is congruent to , triangle is congruent to by the Triangle Congruence Theorem. Since the triangles are congruent, all pairs of corresponding angles are congruent, so angle is congruent to . Since those alternate interior angles are congruent, must be parallel to . Since we define a parallelogram as a quadrilateral with both pairs of opposite sides parallel, is a parallelogram.