How should tone change while shading a round fruit?

Correct answer: Gradually from light to dark

The governing concept is tonal gradation for creating three-dimensional form. Light reaches one side of a round fruit more directly, while the turned-away side receives less light. Therefore the values should transition smoothly from light to dark across the curved surface. Option C is correct. Equal darkness removes form, a dark outline makes the fruit look flat, and no shading cannot show volume.