In quadrilateral ABDC , line segment AB is parallel to line segment CD Which additional piece of information is needed to determine that ABDC is a parallelogram?

In quadrilateral ABDC, AB and CD are opposite sides, and they are already given as parallel. If AB is also congruent to CD, then one pair of opposite sides is both parallel and congruent, which is sufficient to prove the quadrilateral is a parallelogram. Thus, the needed information is that line segment AB is congruent to line segment CD.

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