Which technique is suitable for creating a soft sunset-sky transition in watercolour?

Correct answer: Gradually blend yellow, orange, and red on damp paper

The governing concept is wet-on-wet blending, in which damp paper allows neighbouring transparent colours to merge softly before their edges become fixed. Applying yellow, orange, and red gradually creates a believable sunset transition, so option A is correct. Hard black lines produce abrupt marks, a thick opaque layer conflicts with the transparent nature of watercolour, and adding oil is unsuitable because it changes the medium and can interfere with the paper and paint.