What is the gradual change from light to dark tone called?

Correct answer: Tonal gradation

The governing concept is tonal gradation, a controlled transition from a light value to a darker value across a surface. Option B is correct because it names this gradual change. Texture describes surface quality, a contour defines an edge, and symmetry concerns balanced correspondence. In practice, build the transition with light overlapping layers so that no sudden dark band interrupts the form.