Which combination is best for adding fine details over a dark poster colour area?

Correct answer: Opaque light paint with a fine brush over a dry base

Fine detailing requires control, contrast, and separation between layers. A dry base prevents the new paint from bleeding, opaque light colour contrasts clearly with the dark area, and a fine brush controls small lines and shapes. Hence option A is best. A wet base or watery paint may spread, a broad brush lacks precision, and clean water cannot create a visible detail.