Which mistake is common while showing roundness of form through line?

Correct answer: Drawing straight flat lines on a round form

Correct answer: A. A rounded form has a surface that turns gradually around its volume. To suggest that turning surface with lines, the marks should follow the form’s direction, as contour or cross-contour lines do. Straight, flat lines placed without regard to the curve can make a sphere, cylinder, or other rounded object look stiff and flat. A is correct because it identifies the common mistake of ignoring the form’s turning direction. B is not a mistake; curved lines that follow the form usually strengthen the sense of roundness. C can support the effect when used carefully, although shading alone is not the specific error asked about. D is good working practice, not a mistake. Memory cue: let the line wrap around the form; do not draw across it like a flat board.