Answer:
Deforestation
Explanation:
Green plants are known to undergo photosynthesis to produce food in the presence of sunlight. The green plants use up Carbon dioxide in the photosynthetic process and gives out Oxygen as its byproduct. The Oxygen is the gas that humans inhale to stay alive and for metabolic processes in the body.
Deforestation is the cutting down of trees.
When there is a lot of deforestation going on the amount and quality of oxygen reduces. This reduction becomes harmful to the health and there is also a disruption in the oxygen -carbon dioxide cycle as a result of the deforestation caused by man