How can lifting of the lower colour be prevented while adding a light detail over dark poster colour?

Correct answer: Dry the lower layer completely and use little water with limited strokes

Poster colour can be disturbed when moisture and repeated brushing reactivate or loosen the layer underneath. Allowing the dark base to dry completely, using a relatively controlled mixture, and placing the light detail with few strokes reduces that risk. Therefore option A is correct. A wet base, vigorous rubbing, or excessive water increases movement and makes lifting more likely.