What is the best way to avoid unwanted backruns?

Correct answer: Avoid applying a very wet brush to a partly dry area

Backruns result from a sudden difference in moisture: very wet paint or water enters a neighbouring area that is partly dry and pushes pigment toward its edge. The most reliable prevention is therefore to avoid placing a very wet brush on a drying area and to keep the moisture of adjacent passages reasonably consistent. Adding water everywhere increases risk, white paint changes colour rather than moisture flow, and tilting alone cannot correct the imbalance. Option A is correct.