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: Dental
[{'content': 'Oral malodor is detected by \nSelect and explain. \nA. Gas chromatography, B. Gas Laser, C. Perio-tron, D. Perio-scan', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]