How can the main difference between hard light and soft light be recognized?

Correct answer: By the edge of the shadow

Answer: A, by observing the edge of the shadow. Hard light comes from a relatively small or strongly directed source and commonly creates a distinct shadow with a sharp or clearly defined edge. Soft light is more spread out, often because the source is larger or diffused, and it commonly produces a shadow whose edge changes gradually from dark to light. The shadow edge is therefore a practical visual clue for judging light quality. A is correct because it gives direct evidence of how sharply the light is blocked. B is wrong because paper smell is unrelated to the direction or diffusion of light. C is wrong because a colour wheel organizes colour relationships and does not identify the sharpness of a shadow. D is wrong because brush price has no connection with lighting quality. Other clues, such as the size and softness of highlights, can help, but the question asks for the main recognizable difference. Memory cue: hard light gives a hard-edged shadow; soft light gives a soft-edged shadow.