When can line shading distort the form of an object?

Correct answer: When shading lines move against surface direction

Line shading should help the viewer understand the three-dimensional form of an object. Lines placed in a suitable direction can follow the surface, describe its curve, and show how light and shadow change across it. If shading lines run against the apparent direction or structure of the surface, they may flatten, twist, or otherwise misrepresent the object. The viewer may then read the form incorrectly, even when the individual lines are neat.

The correct answer is option A because shading direction must support the surface form. Lines that follow the object’s structure are more likely to make its volume clear; controlled marks and gradual tonal change can also improve the result. The other choices describe qualities that generally help: following the light, controlling the line, and building tone gradually. Therefore, lines moving against the surface direction can distort the form and make the drawing look unnatural.