Answer: Photosynthesis, Decomposition, Respiration and Combustion
Explanation:
Viruses are not considered alive, because they lack certain aspects that would be considered a living organism.
Oxygen is what animals need in order for Carbon Dioxide to be exhaled while breathing. This is part of what the Respiratory System does. Carbon also enters animals that are in contaminated environments such as living next to a factory or a polluted area.
