Which shape has the property of having opposite sides that are equal in length and parallel?

The rectangle is a shape that maintains the property of having opposite sides that are equal in length and parallel. This definition stems from the characteristics of rectangles as quadrilaterals, where each pair of opposite sides is not only equal in length but also runs parallel to each other. In a rectangle, the four angles are also right angles, contributing to its overall symmetry and structure.

This property is essential in various applications, including geometry, where it helps in calculating area or understanding the relationships between sides and angles. Rectangles are foundational shapes in both theoretical and applied mathematics, which makes their properties vital for problem-solving and geometric understanding.

Other shapes listed do not share this specific combination of properties. A circle does not have sides, while a triangle cannot have opposite sides as it only has three sides total. The scalene triangle, in particular, has all sides of different lengths and does not exhibit the property of having equal opposite sides. Thus, the rectangle emerges as the clear and defining answer here.