Which combination is best for creating a small bright highlight over a dry poster-colour layer?

Correct answer: Small clean brush opaque light paint and limited strokes

The governing technique is controlled opaque layering. A small clean brush places a precise mark, while thick light-coloured paint remains visible over the dry underlying layer. Limited strokes prevent re-wetting or lifting that layer and keep the highlight crisp, so option C is correct. Thin paint on a wet base can spread, a broad wet brush lacks precision, and a brush without paint cannot create a highlight.