Apartial 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, and because they are supplements of the same angle.

which statements should fill in the blanks in the last line of the proof?

∠m is supplementary to ∠n; ∠m is supplementary to ∠o
∠m is supplementary to ∠o; ∠n is supplementary to ∠p
∠m ≅ ∠p; ∠n ≅ ∠o
∠m ≅ ∠o; ∠n ≅ ∠p