The figures opposite angles are congruent, so it is possible to say that the sides are parallel, therefore making it a parallelogram.
Further Explanation:
It is given that the opposite angles of congruent. Let’s say we draw a single diagonal. This diagonal is bisecting the opposite angles of the figure, so the sides are parallel because opposite interior angles are congruent. Then, do the same for the other pair of congruent angles and prove the two sets of opposite parallel sides. This proves the figure is a parallelogram.