How should dots be distributed in stippling to show the volume of a spherical object?

Correct answer: Dense in shadow and gradually wider apart toward the light

Stippling models form through tonal density: closely spaced dots create a darker value, while wider spacing creates a lighter value. On a sphere, the shadow side needs denser dots and the light side needs progressively fewer dots, so D is correct. Uniform dots flatten the form, boundary-only dots show outline, and reversing density contradicts light-and-shade logic.