In which situation may it be suitable to keep a shape boundary soft?

While showing cloud, smoke, or mist

The governing concept is the expressive use of edges or boundaries. A hard, sharp boundary makes an object appear definite, solid, and clearly separated from its surroundings, while a soft or blurred boundary suggests uncertainty, atmosphere, vapor, distance, or gradual blending. Option A is correct because clouds, smoke, and mist do not normally have rigid outlines; a softened edge communicates their changing and diffuse nature. Option B requires a precise boundary so that the sign can be recognized quickly. Option C generally depends on clean geometric edges for clarity and reproduction. Option D represents a solid manufactured object whose structure is better shown with firm edges. Thus, boundary quality should match the visual character of the subject.

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