A long line made with a liner brush becomes thick and then thin although the artist wants uniform width. What is the main correction?

Correct answer: Maintain even pressure and speed

Uniform line width depends mainly on steady pressure, consistent travel speed, and a controlled brush angle. Pressing harder spreads the bristles and makes the mark thicker; moving faster or lifting slightly makes it thinner. Therefore option D is the main correction. Changing colour has no mechanical effect, wetting the paper may reduce control, and merely adding paint cannot compensate for uneven pressure and motion.