Which method is better for creating a dark tone?

Correct answer: Build several light layers

The governing concept is controlled layering in graphite shading. Applying several light layers gradually increases the amount of graphite while preserving control over the value and keeping the surface more even. Therefore option B is correct. Pressing very hard at once can dent or polish the paper and may create a patchy mark. An eraser removes graphite, and folding the paper has no role in creating a dark tone.