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': "CO2 in air is measured by \nSelect and explain. \nA. Kieffer test, B. EPKJMAN'S test, C. Silvered thermometer, D. Orthotoludene test", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]