Where is the most appropriate use of a hard edge in a sketch?

Correct answer: At the focal area or a clear contact region

Edge control is a way of directing attention and describing form. A hard, sharply defined edge is most useful at the focal area or where one object clearly touches another, because it attracts the eye and clarifies contact. Thus option B is correct. Using hard edges everywhere creates a stiff drawing; backgrounds usually need softer edges, and reflected light alone does not determine edge hardness.