Final answer:
In the carbon cycle, carbon dioxide is released into the atmosphere by various processes including respiration by animals.
Step-by-step explanation:
During the carbon cycle, carbon dioxide is released into the atmosphere by various processes.
Plants add carbon dioxide during cellular respiration, which is the process of breaking down glucose to release energy. Animals also release carbon dioxide through respiration when they break down glucose to obtain energy. Fossil fuel combustion, decomposition of dead organisms, and geological activities like volcanic eruptions also contribute to the release of carbon dioxide into the atmosphere.
Therefore, the correct answer is c. animals.