In scumbling the underlying colour is not visible at all. What should the artist change?

Correct answer: Use less upper colour with light irregular strokes

Scumbling is based on broken, irregular application in which small gaps allow the underlying colour or texture to show through. If the lower layer has disappeared, too much opaque paint or pressure has probably been used. Option A is correct: reduce the paint load, use light pressure, and make irregular strokes. A thick coat, wetter surface, or continuous pressing would cover the underlayer even more completely.