A student used only black in all shadow areas and every object began to look equally heavy. Which principle was ignored?

Correct answer: Considering each object's local colour and temperature

The governing principle is that a shadow is affected by local colour, surrounding light, and warm–cool temperature, not merely by blackness. Applying identical black to every object suppresses hue differences and makes all forms appear equally heavy, so A is correct. Paper size, brush-washing time, and letter height may affect other aspects of an artwork, but they do not explain the loss of varied shadow colour in this example.