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: Forensic Medicine
[{'content': 'In low concentration of carbon monoxide (40/) the commonest symptom is : \nSelect and explain. \nA. Nausea, B. Headache, C. Muscular weakness, D. None', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D i.e. None', 'role': 'assistant'}]