This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and health, Subject name: Social & Preventive Medicine
True about global warming is - 
Select and explain. 
A. CO2 is the major greenhouse gas, B. Stratosphere ozone layer is harmful, C. CFC increases stratosphere ozone layer, D. Kyoto protocol called for 20% reduction in green house effect
A: CO2 is the major greenhouse gas
Answer: A: CO2 is the major greenhouse gas 
Explanation: CO2 is the major greenhouse gases which are mainly emitted from the combustion of fossil fuels Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 794