Geometry

Question Analysis:
This question tests the application of the parallelogram theorem to generalized side lengths.
The main focus is to recognize that alternating side lengths () imply opposite sides congruent.

Key Concept Explanation:
In a quadrilateral with side lengths  in order, the first and third sides (a) are opposite, and the second and fourth sides (b) are opposite.
Both pairs are congruent, satisfying the parallelogram criterion.

Step-by-Step Solution:
Interpret the side order: , , , 

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