Which beginner exercise is most useful for practising blending?

Correct answer: Create a gradual transition between two colour bands

The governing concept of blending is a controlled, gradual transition rather than a sudden boundary. Creating a transition between two colour bands lets a beginner practise pigment quantity, water balance, brush pressure, stroke direction, and the timing of overlapping wet areas. Option D directly trains these skills. Black lines, cutting paper, and writing brush names may be useful elsewhere, but they do not practise smooth colour transitions.