When is it more suitable to apply the next stroke while creating a smooth gradation?

Correct answer: While the first stroke is still damp

The governing concept is wet or damp blending for a gradual tonal transition. When the first stroke is still damp, the next stroke can merge gently with it, reducing a sharp boundary and producing a smoother gradation. Therefore option B is correct. A fully dry stroke tends to leave a visible edge, while torn paper or a dry brush cannot create controlled blending.