Which line is better to show turning of a form's surface?

Correct answer: Cross contour line

Direct answer: A, a cross-contour line. A contour line follows the edge of a form, while a cross-contour line travels across the form and follows the direction in which its surface turns. On a sphere, for example, curved lines wrapping around the surface help the viewer understand its roundness. On a cylinder, the lines can show the circular direction of the surface. B only describes an outer boundary and cannot explain much about the surface turning inside the form. C is not a standard art term for this purpose; ‘value’ refers to lightness or darkness. D is not a recognised drawing method. A is therefore correct because it describes surface direction and volume together. Memory cue: contour goes around the edge; cross-contour goes across the surface.