Which correction is most useful next time if colour spreads outside the edges?

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

The governing concept is edge control during colour filling. A small brush gives greater precision, while reduced moisture prevents excess paint from flowing beyond the boundary. Therefore, option A is the most useful correction. More water increases spreading, fast long strokes reduce control near corners, and pouring paint from above makes accurate placement impossible. Working slowly near the edge and using a suitable paint load improves neatness.