Which type of line may be more suitable to show a hard object like a machine or metal?

Straight and clear lines

The governing concept is line quality as a way to communicate material and structure. Machines and metal objects commonly have firm edges, planes, joints, and geometric construction. Straight, clear, and controlled lines can describe those boundaries more convincingly, so option A is correct. Very soft wavy lines are more suitable for flexible, flowing, or delicate forms and may make a machine appear less rigid. Directionless light lines do not clearly define a solid structure, while flower-like rounded lines suggest a different organic subject. This does not mean every metal object must be drawn only with ruler-straight marks: curved pipes, handles, reflections, and perspective may require curves or varied weight. The important point is that the dominant structural edges should be deliberate, stable, and clearly related to the object’s hard construction.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Line.