Suppose both pairs of opposite sides of a quadrilateral are parallel. Which angles of the quadrilateral must be supplementary? A. Pairs of opposite angles are complementary; the sides of the quadrilateral are transversals and the interior angles are on the same side of the transversal are not congruent.

B. Pairs of consecutive angles are supplementary; the sides of the quadrilateral are transversals and the interior angles are on the same side of the transversal.