Which method is more suitable for making a clean edge in watercolour?

Correct answer: Apply paint on dry paper

The relevant watercolour principle is wet-on-dry painting. When paint is applied to a dry sheet, the water and pigment spread less freely, so the boundary remains more controlled and clean. Therefore, option A is correct. Very wet paper encourages diffusion and soft, blurred edges; dipping the paper gives no useful control, and a dripping brush adds unwanted blooms or puddles. Use a moderately loaded brush and a steady stroke for a crisp edge.