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
Gas causing green house effect ? 
Select and explain. 
A. CO2, B. Methane, C. Sulfur hexafluoride, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: Ans. is 'd' i.e., All of the above