Answer:
Line DB and AC intersect at point E.
∠AEB = ∠DEC because they are vertical angles.
∠EAB and ∠ECD are alternate interior angles because AB and CD are parallel lines and line AC crosses through both parallel lines.
m∠EAB = m∠ECD because they are alternate interior angles.
ΔABE ≅ ΔCDE because there are two sets of congruent angles.