Explanation:

- Water Vapors: Water vapor is a natural greenhouse gas but is not directly released in significant amounts from volcanic eruptions, animal respiration, deforestation, or burning fossil fuels. It primarily originates from evaporation and transpiration.

- Chlorofluorocarbons (CFCs): These are synthetic greenhouse gases used in refrigerants and aerosols and are not typically associated with the processes listed.

- Methane: Methane is released from animal digestion (especially ruminants like cows) but is not a major component of volcanic emissions, burning of fossil fuels, or deforestation.

- Sulfur: While sulfur compounds can be emitted from volcanic eruptions, they are not significant greenhouse gases and are not related to animal respiration, deforestation, or fossil fuel burning.

- Carbon Dioxide: [Correct Answer] Carbon dioxide is a major greenhouse gas released by volcanic eruptions, animal respiration, deforestation, and especially the burning of fossil fuels. It significantly contributes to the greenhouse effect and climate change.