<span>The diagonals are congruent.
Since all rectangles are also parallelograms, let's check which option provides that little extra kick to make a parallelogram a rectangle.
The diagonals bisect each other.
* This would be wrong. The perpendiculars bisect each other in all parallelogram. So this won't make a parallelogram a rectangle and this is a bad choice.
The diagonals are congruent.
* This would work. Since the diagonals are congruent, they along with the parallelogram will form 4 congruent triangles. And the only way all 4 triangles can be congruent is if they're all right triangles. So this is the correct choice.
The diagonals are congruent and perpendicular.
* Sorry, the diagonals in a rectangle are generally not perpendicular. The only time that they are perpendicular is if the rectangle is also a square. So this is a bad choice.
The diagonals bisect each other and are perpendicular
* This is only true if the rectangle is a square. So it's over specific and therefore a bad choice.</span>
