Answer
1. In a parallelogram, opposite sides are parallel.
2. Thus, two opposite angles in parallelograms are corresponding angles.
3. Corresponding angles are congruent.
4. Thus, opposite angles of parallelograms are congruent.
5. The sum of the angles in a parallelogram is 360 degrees.
6. If opposite angles are congruent and the sum is 360 degrees, then consecutive angles are supplementary.
