Which method is more effective than filling a dark fur area with only long black strokes?

Correct answer: Layer short directional strokes of different dark tones

The governing concept is layered brushwork for texture and depth. Short strokes in related dark tones, placed in the direction of the fur and built in layers, preserve variation, overlapping fibres, and subtle light differences. A single black mass or long uniform marks flatten the area and hide the structure. White dots alone are too isolated, while erasing strokes removes the texture rather than describing it, so B is correct.