1. Checking the angles (rectangle four 90º angles)
Parallelogram
2. The diagonals bisect each other (parallelogram) and for rectangles, they bisect at different angles.
1) There is one possible way to verify whether a parallelogram is a rectangle or not.
2) You can check the angles. A rectangle has four right angles and a pair of parallel and congruent sides.
3) In addition to this, we can state that the diagonals of a parallelogram bisect themselves while in a rectangle they bisect each other at different angles:
So the answer is:
1. Checking the angles (rectangle four 90º angles)
Parallelogram
2. The diagonals bisect each other (parallelogram) and for rectangles they bisect at different angles.