<span>chlorophyll CO2 H2O O3 C2O anaerobic conditions light ammonium triphosphate</span>
Answer: I believe the answer is D because I know that you can't kill a eagle in the U.S. because it is a protected species.
The answer is C. nitrogen.
Plants are main producers in ecosystems so, primary productivity of ecosystems depends on them. Carbon is necessary for plants, but it is widely present in plants. On the other hand, calcium and sodium are not as essential. However, nitrogen is important for plants because it is necessary to make proteins. Proteins take part in many different processes such as photosynthesis (this is actually primary productivity). But, nitrogen is not available to plants, they cannot absorb it simply from the air but rely on some symbiotic bacteria which are able to.
Answer: The food
Explanation: the independent variable is the one to be changed and in this case, it is the food
