Which of these shapes is classified as a three-dimensional object?

A cylinder is classified as a three-dimensional object because it has length, width, and height. Unlike two-dimensional shapes, which only have length and width, a cylinder extends into space, giving it volume. This means it occupies space and can be measured in three dimensions—having cylindrical sides, a circular base, and a specific height. The other options, such as the circle, square, and triangle, are all examples of two-dimensional shapes that only have length and width. They can be drawn on a flat surface but do not possess depth or volume. This fundamental distinction between two-dimensional and three-dimensional shapes is essential in geometry.