How can naturalness appear in hair or grass made with line?

Correct answer: Through subtle variation in direction, length, and density

Direct answer: A, through subtle variation in direction, length, and density. Natural hair and grass do not grow as a perfectly repeated machine-made pattern. Some strands bend, overlap, separate, become shorter, or appear darker because of their grouping and direction. In a drawing, the artist should first observe the general flow of the hair or grass, then add groups of lines following that flow. Small controlled changes in length, spacing, angle, and darkness prevent an artificial appearance. B is wrong because identical lines look mechanical and repetitive. C is wrong because one direction and parallel spacing cannot show the varied growth of a natural surface. D is wrong because a solid colour removes the line-based indication of strands and texture. Variation should be controlled, not random; too much disorder can also reduce clarity. Memory cue: natural texture needs organised variety, not perfect repetition.