Which property distinguishes a rectangle from a general parallelogram?

• A. Opposite sides are parallel and equal
• B. Diagonals are perpendicular
• C. Opposite angles are supplementary
• D. All angles are right angles

Answer: (D)

All four angles being right angles defines a rectangle. In any parallelogram, opposite sides are parallel and equal, and consecutive angles are supplementary. If one angle is a right angle, the angle next to it must be 180 minus 90, which is also 90. Repeating this around the shape shows all angles are 90 degrees, so the figure is a rectangle. The other properties aren’t unique to rectangles: having opposite sides parallel and equal is true for all parallelograms; diagonals perpendicular is not a general feature of rectangles (it occurs in special cases like a square); and opposite angles being supplementary describes parallelogram behavior but doesn’t force all angles to be right.