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

For any quadrilateral to be a parallelogram

i) either both the pairs of opposite sides must be equal

ii) Both the pairs of opposite sides must be parallel

iii) Opposite pairs of angles must be equal

iv) Diagonals must bisect each other.

v) A pair of opposite sides must be parallel and equal

Here we are already given that AB || CD

So either we should be given that AD || BC

or we must be given that AB = CD

Here it is given AB = CD as an option.

So Option A) or the first option is the right answer that AB ≅CD is needed to prove ABCD is a parallelogram.