Which practice is useful for keeping a poster background uniform?

Correct answer: Keep the paint and water ratio consistent

The governing concept is consistency of paint application. Keeping the paint-to-water ratio steady gives each brushload a similar thickness and colour strength, helping the background appear even. Different water amounts create light and dark patches; using unmixed paint can cause uneven pigment, and repeated rubbing over wet colour disturbs the layer. Controlled, parallel strokes also support a uniform finish.