Which technique is most effective for showing light on a rough tree trunk?

Correct answer: Controlled dry brushing of a light colour over raised texture

The governing concept is that brush direction, paint load and surface texture work together to show light. In dry brushing, a relatively dry brush carrying a light colour touches mainly the raised parts of rough bark, so those ridges catch the highlight while recesses remain darker. A white wash covers everything evenly, a black outline describes shape only, and complete wet blending removes the useful texture contrast. Therefore, option A is correct.