Answer:
The correct answer option is D. perpendicular.
Explanation:
The diagonals of a square are perpendicular.
A square is a shape which has parallel sides (not parallel diagonals), has diagonals that are perpendicular bisector of each other and also its diagonals are congruent.
So according to these properties of square, options A, B and C are wrong and we are left with option D which is the correct one.