Ally is a junior high student who has just learned about the carbon cycle in school. She is concerned about the environment and decides to construct a model of the carbon cycle in her community. What could both add and remove carbon from the atmosphere in the model?

The image shows an arrow pointing from the animal to the atmosphere, an arrow from the atmosphere to the tree, an arrow from the tree to the atmosphere, and an arrow from the automobile to the atmosphere. The illustration shows a car, a deer, and some trees. Arrows go from all three to a label: CO2. Another arrow points down from the CO2 label to the trees.

A. a car
B. a deer
C. an insect
D. a tree