To prove that quadrilateral ABCD is a parallelogram, you can utilize the property about opposite sides of a parallelogram. The correct response is:
Opposite sides of the figure are congruent.
In a parallelogram, a fundamental property is that both pairs of opposite sides are equal in length. If you have the lengths of the sides, showing that AB = CD and AD = BC will suffice to prove that ABCD is a parallelogram. If the lengths match as stated, then you can conclude that quadrilateral ABCD is indeed a parallelogram based on this property.