Answer:
∠B and ∠C are supplementary
Step-by-step explanation:
You want to know the relationship between angles B and C in trapezoid ABCD, where AB║CD.
Consecutive interior angles
Where a transversal crosses parallel lines, the consecutive interior angles are supplementary. The line between the parallel bases of a trapezoid is one such transversal, and the two interior angles it creates are "consecutive interior angles".
This means angles A and D are consecutive interior angles, as are angles B and C.
Angles B and C are supplementary.
