In quadrilateral abdc, ab ∥ cd. which additional piece of information is needed to determine that abdc is a parallelogram? a) ab ≅ cd b) ac ≅ bd c) ab ⊥ bd d) cd ⊥ bd

Since the definition of a parallelogram literally says that it's a quadrilateral with 2 parallel sides, we have AB || CD so the 2 other sides (AC and BD) need to be either similar or parallel (either works, due to that if they're similar we can prove that since AB || CD that they're parallel). B is our answer