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Based on the above diagram, the following statement holds true.
If ∠A≅∠C and ∠B≅∠D, then ABCD is a parallelogram.
Assume that ABCD is a quadrilateral with opposite congruent angles. It should be noted that congruent angles have the same measure. Then, let x∘ be the measure of ∠A and ∠C, and y∘ be the measure of ∠B and ∠D.