posted by Faith .
Suppose both pairs of opposite sides of a quadrilateral are parallel. Which angles of the quadrilateral must be supplementary?
I do not understand what this question is asking and how I should answer. Please help if you can!
What shape do you get when you draw a quadrilateral with opposite sides parallel?
Study the properties of such a quadrilateral related to the adjacent angles.
Alternatively, you can consider that adjacent interior angles of the quadrilateral are always between parallel lines. What can you say about the sum of interior angles between two parallel lines intersected by a line (the included side in the case of the quadrilateral).