Final answer:
The best balance to maintain low levels of carbon dioxide in the atmosphere is a large volume of plants with a small number of carbon sources.
Step-by-step explanation:
The best balance to maintain low levels of carbon dioxide in the atmosphere is C. a large volume of plants with a small number of carbon sources. By having a large volume of plants, more carbon dioxide can be absorbed through photosynthesis. However, having a small number of carbon sources ensures that there is not an excess of carbon dioxide being released back into the atmosphere.