Lauren made the plan shown for proving that quadrilateral abcd with ab ≅ cd and bc ≅ da is a parallelogram, by showing that the opposite angles are congruent. plan: draw in diagonals ac and bd. the given information and the shared side ac along with the reflexive property can be used to prove by the sss congruence postulate. using cpctc, the same can be done for using the given information and the shared side bd¯¯¯¯¯¯¯¯. this will lead to therefore, abcd is a parallelogram because opposite angles are congruent.