1. a quadrilateral is a parallelogram if both pairs of ________ sides are _______
2. a quadrilateral is a parallelogram if both pairs of _______ angles are ________
3. a quadrilateral is a parallelogram if both pairs of _______ angles are ________
4. a quadrilateral is a parallelogram if the _________ bisect each other
5. a quadrilateral is a parallelogram each __________ divides a parallelogram into two ___________
6. a quadrilateral is a parallelogram if one pair of opposite sides are both ________ and ________​