What is the most likely reason if a dry-brush texture becomes excessively rough in poster colour?

Correct answer: The brush had too little paint and too much pressure

The governing concept is controlling dry-brush friction and paint load. When the brush carries too little paint and is pressed too firmly, its bristles drag across the surface, producing harsh, broken marks and an excessively rough texture. A controlled result needs a moderate paint load and light, steady pressure. A clean brush or flat paper does not by itself create this problem, while sufficient water reduces dry-brush roughness rather than causing it. Therefore, option A is correct.