The correct option is B Balance of oxygen and carbon dioxide by plants and animals.
∙ Plants, during the process of photosynthesis, consume carbon dioxide present in the air and produce oxygen along with their food.
∙ Plants also take in oxygen during respiration but the amount of oxygen produced during photosynthesis is more than what they take in.
∙ So, plants give out oxygen to the atmosphere which is consumed by animals. Animals release carbon dioxide. So, there is a balance of oxygen and carbon dioxide in the atmosphere maintained by plants and animals.