Equal-sized dots are required in stippling but some dots become elongated. What is the cause?

Correct answer: The brush is being dragged instead of lifted straight

Stippling creates dots through a controlled press-and-lift action. When the brush is lifted vertically, its contact remains approximately circular; when it is dragged before leaving the surface, the contact travels sideways and produces an elongated mark. Option D is therefore correct. Paint purity, paper brightness, and brush size may affect appearance or scale, but they do not explain the directional stretching of individual dots.