C <<<< Simple answer
Rectangles have parallel lines and so do squares. It's not a distinguishing set of characteristics.
Both rectangles and squares have right angles. It does not distinguish them.
To give both squares and rectangles the property of having convex angles is to say that all the angles are less than or equal to 180o. That's true, but it does not distinguish the two figures.
The only thing that does is that a square is a rectangle with 4 equal sides.
C <<<< answer.