What helps most in making a ball look like a round form?

Gradually changing shading

The governing concept is tonal modelling of a curved surface. A ball looks round when the viewer can see a controlled movement from the lightest area through middle values toward a darker shadow, with the changes following the curvature of the surface. Option C is correct because gradual shading creates the illusion that the surface turns away from the light and possesses volume. Option A supplies only a label, not visual evidence. Option B keeps every part equally flat and therefore suppresses depth. Option D changes the paper rather than representing the object. The artist should also keep the highlight, reflected light, and cast shadow consistent with one light source, but the essential cue asked here is progressive shading.

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