properties of quadrilaterals
Check the final answer first, then review the worked steps.
Problem
properties of quadrilaterals
Step-by-step solution
If consecutive angles are supplementary, then adjacent sides are parallel (e.g., $\angle A + \angle B = 180^\circ$ implies $AD \parallel BC$). Since this holds for all pairs, opposite sides are parallel, which defines a parallelogram.
Answer
A. True