What is the greatest technical problem when filling a very small area with a large brush?
The governing concept is tool-to-area suitability. A large brush has a broad contact area and may carry more paint or water than a tiny space can safely receive. Its bristles can cross the boundary before the painter can stop, making edges inaccurate and causing spills. Option D is correct. Brush size alone does not lighten or purify colour, and paper drying is not the main technical problem in this situation.