This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Among the following, which of the following is/are the greatest contributor/contributors to global warming as a consequence of human activities and life style ? 
Select and explain. 
A. Carbon dioxide, B. Chlorofluorocarbons, C. Methane, D. Ozone
A: Carbon dioxide
Answer: A: Carbon dioxide 
Explanation: None