Cross-contour lines are most useful for explaining what?

The three-dimensional turn of an object’s surface

Cross-contour lines are drawn across or around an object rather than only along its outer boundary. They follow the imagined surface and help the viewer understand how that surface turns through space. On a sphere, for example, curved cross-contours wrap around the form; on a cylinder, they can show circular swelling and direction. Option A is correct because these lines explain three-dimensional curvature, volume, and the orientation of a surface. The other options concern cost, physical frame weight, or labeling, none of which can be communicated by cross-contours. Their usefulness depends on observing the form carefully: the lines should bend and change according to the object, not be added as random decoration. They are therefore an important application of line for describing form.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Line.