Which of the following is a valid reason why the quadrilateral shown below is a parallelogram? a. both pairs of opposite sides are parallel. b. all pairs of consecutive angles are complementary. c. both pairs of opposite angles are congruent. d. all pairs of consecutive angles are supplementary.

A. Both pairs of opposite sides are parallel.  

C. Both pairs of opposite angles are congruent.  

D. All pairs of consecutive angles are supplementary

Step-by-step explanation:

Every parallelogram has these three properties. If only one pair of opposite sides is required to be parallel, the shape is a trapezoid, not a parallelogram. If a pair of consecutive angles are supplementary, i. e., their addition is equal to 180°, then all pairs of consecutive angles are supplementary, and consequently, both pairs of opposite angles are congruent, that is, they have the same measure.