Which method is most useful to make a flat circle look like a ball?

Correct answer: Applying value and shadow

A flat circle shows only a round outline, so it normally appears two-dimensional. A ball is a sphere, and it appears three-dimensional because light and dark areas suggest curved volume. Gradual changes from a lighter area toward a darker shadow, together with a cast shadow when appropriate, make the surface seem to turn away from the light. This is a visual illusion created on a flat page through value relationships.

Option A is correct because applying value and shadow changes the circle into a convincing image of a sphere. Cutting paper changes the object physically rather than modelling it in a drawing, while writing a title does not create depth. Removing all colour can produce a monochrome study, but without light and dark variation it will not make the circle look like a ball. Careful shading is therefore the essential method.