Which option correctly uses a light source to make a form believable?

Correct answer: The highlight and cast shadow follow the direction of light

The governing concept is consistency between light direction, highlights, form shadows, and cast shadows. Before shading, the artist should decide where the light is coming from. Surfaces facing that source generally receive more light, a highlight may appear on a suitable curved or reflective area, the turned-away side becomes darker, and the object can cast a shadow onto the supporting surface in a related direction. Option A is correct because it connects both highlight and cast shadow to the same light source. Option B produces arbitrary lighting, while option C confuses a cast shadow with a form shadow; a cast shadow falls outside the object on another surface. Option D rejects the basic cause of shading. The exact softness varies with the size and distance of the source, but directional consistency is essential for believable form.