we are supposed to find
Which of these properties is enough to prove that a given parallelogram is also a Rectangle?
As we know from the theorem, if the diagonals of a parallelogram are congruent then the parallelogram is a rectangle.
The other options The diagonals bisect each other is not sufficient because in parallelogram diagonals always gets bisected , parallelogram becomes rectangles only if both the diagonals are of same length.
In a parallelogram The opposite angles and opposite sides are always equal.
Hence the correct option is
The diagonals are congruent.