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
[{'content': 'Which one of the following is not a greenhouse gas ? \nSelect and explain. \nA. Carbon monoxide, B. Methane, C. Nitrous oxide, D. Water vapour', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]