The correct answer is C. Photosynthesis.
Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy in the form of sugar. This process is essential for life on Earth, as it removes carbon dioxide from the atmosphere and produces oxygen.
Lightning is a natural process that occurs when electrical charges build up in the atmosphere and are discharged. Lightning does not remove carbon dioxide from the atmosphere.
Deforestation is the clearing of forests for other uses, such as agriculture or development. Deforestation increases the amount of carbon dioxide in the atmosphere, as trees are no longer able to absorb carbon dioxide from the air.
Burning fossil fuels is a human activity that releases carbon dioxide into the atmosphere. Fossil fuels include coal, oil, and natural gas. Burning these fuels releases carbon dioxide that was stored underground for millions of years.
In conclusion, the only process that acts to remove carbon dioxide from the atmosphere is photosynthesis.