Why can leaving guide lines dark in a drawing be harmful?

They can distract from the final form

Guide lines are construction marks used temporarily to plan proportion, alignment, perspective, or placement. Their governing purpose is to support the drawing process, not to compete with the finished contours and important details. If they remain dark, the viewer may notice the planning framework instead of the final form, and the object can look confused, dirty, or visually fragmented. Option A is correct because strong guide lines can distract from the intended image. Option B is too absolute and usually false; C confuses a graphite or ink mark with colour, while D is impossible because marks do not clean paper. Artists commonly keep construction lines light, erase them carefully, or integrate only those that contribute to the final design.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Line.