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
[{'content': "Other than nitrogen and oxygen, which one of the following is the most abundant gas in the eah's atmosphere? \nSelect and explain. \nA. Argon, B. Carbon dioxide, C. Hydrogen, D. Methane", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Atmosphere composition Nitrogen 78% O2 21% Argon 0.9% CO2 0.03%', 'role': 'assistant'}]