Which element of art seen in a drawing of a cube demonstrates depth through shading contour lines or highlights?

The element of art that demonstrates depth in a drawing of a cube is shading. By using varying degrees of lightness and darkness, shading creates the illusion of three-dimensionality, making the cube appear more realistic. Contour lines can outline the shape but do not convey depth as effectively as shading does. Highlights, which indicate where light hits the surface, further enhance this sense of depth and volume.