What is the limitation of moving the brush only with the fingers during a very long expressive stroke?

Correct answer: Movement may become short and stiff, so arm or shoulder involvement may be needed

The governing principle is matching the scale of body movement to the length of the mark. Fingers provide precise, small movements, but relying on them alone for a long expressive stroke can produce a cramped, interrupted, or stiff line. The wrist, elbow, or shoulder can create broader and smoother motion. Finger-only movement does not automatically change paint thickness or brush capacity. Thus option D correctly states the limitation.