If poster colour repeatedly spreads beyond a boundary which technique is most suitable?

Correct answer: Use a small brush with less paint near the boundary

The governing concept is edge control through brush size and paint loading. A small brush gives better precision, while a reduced amount of paint prevents flooding across the boundary. Thus, option A is correct; working from the inside toward the edge also helps maintain a clean outline. More water increases spreading, a broad brush pressed firmly deposits excess paint, and tilting the paper does not provide reliable control of the wet colour.