n the blank. If a quadrilateral is a parallelogram, then opposite If a quadrilateral is a parallelogram, then If a quadrilateral is a parallelogram, then consecutive supplementary. If a quadrilateral is a parallelogram, then opposite sides are If a quadrilateral is a parallelogram, then diagonal Sides Diagonal are parallel. Congruent angles are congruent. Opposite are Bisect Consecutive each other.