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. If all opposite angles are congruent, then all opposite sides are congruent.
6. If opposite angles and opposite sides are congruent, then the diagonals will bisect each other.
