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- If pairs of opposite sides of a quadrilateral are congruent then that quadrilateral is a parallelogram.
- If both the pairs of opposite angles of a quadrilateral are congruent then it is a parallelogram.
- If the diagonals of a quadrilateral bisect each other then it is a parallelogram.
- A quadrilateral is a parallelogram if a pair of its opposite sides is parallel and congruent.