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
Global warming, which is true: 
Select and explain. 
A. CO2 is the major green house gas, B. Stratosphere ozone layer is harmful, C. CFC increases the zone of stratosphere, D. KYOTO protocol set the target of net reduction of 20 green house gas emission
A: CO2 is the major green house gas
Answer: A: CO2 is the major green house gas 
Explanation: CO2 is the major green house gas