A partial proof was constructed given that MNOP is a parallelogram. By the definition of a parallelogram,MN ∥ PO and MP ∥ NO.Using MP as a transversal, ∠M and ∠P are same-side interior angles, so they are supplementary.Using NO as a transversal, ∠N and ∠O are same-side interior angles, so they are supplementary.Using OP as a transversal, ∠O and ∠P are same-side interior angles, so they are supplementary.Therefore, __________________ because they are supplements of the same angle.