The Single Most Significant Human-Caused Contribution to the Worldwide Increase

The single most significant human-caused contribution to the worldwide increase in atmospheric carbon dioxide levels is

A) acid rain and the subsequent chemical reactions that release carbon dioxide from the soil.
B) the use of nitrogen supplements that accelerate decompositional activity and recycle carbon before it can become sequestered in the soil.
C) the burning of fossil fuels and the subsequent emission of carbon dioxide.
D) deforestation and the subsequent decline in photosynthesis.