What is necessary to maintain consistent thickness in poster-colour lettering?

Correct answer: Consistent brush pressure and controlled movement

The governing concept is uniform lettering through controlled brush technique. Keeping pressure steady and moving the brush at a consistent speed helps deposit a similar amount of poster colour along each stroke, so the letters retain even thickness. Option D is correct. Changing brushes, adding excessive water, or using a wet background does not reliably control letter width and may create uneven marks.