Which method is suitable for creating a soft cloud effect in watercolour?

Correct answer: Spread light colour on a wet surface

The governing concept is soft diffusion in a wet-on-wet watercolour application. A lightly damp surface lets a pale wash spread gradually, so its edges remain gentle and cloud-like; therefore option A is correct. Hard dark lines on dry paper create sharp marks, cutting the paper changes its shape rather than painting a cloud, and filling the area with black destroys the light, airy quality. Leaving some paper light also helps suggest cloud brightness.