Which of the following is a property of a rectangle?

A rectangle is defined by its specific geometric properties. One of the fundamental characteristics is that its opposite sides are equal in length and also parallel to each other. This means that for any rectangle, if one pair of opposite sides has a certain length, the other pair will have the same length. Additionally, this parallelism helps establish not only the shape of the rectangle but also contributes to the right angles formed at each vertex.

The property described where all sides are equal refers to a square, which is a specific type of rectangle with additional constraints. The notion that all angles are acute does not apply to rectangles, as they have four right angles (90 degrees). Lastly, the attribute stating that only one pair of sides is parallel contrasts with the definition of a rectangle, as both pairs of opposite sides must be parallel. Therefore, the property of opposite sides being equal and parallel is indeed a defining feature of a rectangle.