a). Decrease.
Plants can absorb carbon dioxide from the air in the process of photosynthesis, where they make food using carbon dioxide and sunlight. Therefore, the carbon dioxide in air would decrease.
b). Increase.
Burning of fossil fuels, or combustion, releases not only carbon dioxide, but also other greenhouse gases like nitrous oxides. That's why people nowadays recommend renewable energy like solar energy instead of nonrenewable energy produced by burning of fossil fuels. So, the answer is increase.
c). Increase
During respiration, animals release carbon dioxide and breathe in oxygen. Carbon dioxide are waste to the body. Therefore, the more animals there are, the more carbon dioxide we exhale each and every day.
d). Increase.
Deforestation is the removal of large scale of forest and trees. As we already said in part a, plants (or trees) absorb carbon dioxide for photosynthesis. Therefore, if the trees are removed, there would be less carbon dioxide being absorbed and removed from the atmosphere.
