Analysis: The problem tests the understanding of perpendicular lines within geometric shapes. Shapes like squares and rectangles inherently have perpendicular sides. The task implicitly requires students to recognize these right angles and visually extend the relevant sides. The other shapes, such as the parallelogram and general triangle, do not have perpendicular sides by definition (unless they are specific types like a right-angled triangle, where two sides are perpendicular). The right-angled triangle does have perpendicular sides. The trapezoid shown does not have perpendicular sides unless it's a right trapezoid, which this one does not appear to be.