How may a surface appear when tone changes suddenly from light to very dark?

Correct answer: Hard or angular

The governing concept is the relationship between tonal transitions and form. A sudden change from light to very dark creates a sharp boundary between values, which makes the surface appear to turn abruptly, like a hard plane or angular edge. Thus, option D is correct. A soft, rounded form normally needs gradual transitions through middle tones. Transparency and colourfulness are unrelated to the abruptness of a graphite value change. Use sharp changes for hard planes and smoother changes for curved forms.