Answer:
D. Opposite angles are congruent
With option A, we can see that it is clearly wrong, in a parallelogram, only the opposite sides are congruent, if all of the sides are congruent then the shape is more likely to be a square or a rhombus.
With option B, only the opposites angles are congruent. If all four angles are congruent, that will be more likely to be true when we consider a square or a rectangle.
With option C, it is also wrong, unless the shape is a rhombus, square or rectangle.
That leaves us with the last option which is D.
