Christian's drawing at the top has a lot of character with a complementary color scheme of tertiary colors (yellow-green and red-violet or magenta). The quirky shapes are complemented by expressive rendering of the values and simple, stylized marks in the background.
David's drawing too exhibits lively mark-making and bold highlights. His drawing illustrates the power and importance in using the white pencil.
Veronica's drawing exhibits very acidic and electrified complementary colors. Again the mark-making supports the colors in a very active way. In addition, notice how she has placed proportional amounts of each color across the composition to reinforce unity.