Which of the following are not sufficient to prove that a quadrilateral is a parallelogram? i. two pairs of opposite angles congruent. ii. a pair of adjacent angles are supplementary. iii. both pairs of opposite sides are congruent. iv. a pair of opposite angles congruent and a pair of opposite sides congruent. v. both pairs of opposite sides are parallel. vi. a pair of opposite sides parallel and the other pair of opposite sides congruent. vii. one pair of opposite sides are both parallel and congruent. viii. the diagonals bisect each other. a. iv and vii only b. ii, vi, and vii only c. ii and vi only d. ii, iv, and vii only