Why is it necessary to understand surface direction rather than seeing contour only as an outer boundary?

Correct answer: It allows the line to express volume and turning of the form

The correct answer is A. When contour marks respond to the direction in which a surface turns, they communicate the form’s volume, planes, and curvature instead of merely enclosing a flat silhouette. Colour quantity, background whiteness, and physical weight cannot be inferred from contour direction alone. Thus surface awareness makes the drawing more three-dimensional.