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: Physiology
[{'content': 'Concentration of methemoglobin to appears cyanosis \nSelect and explain. \nA. 5 gm/ dl, B. 2 gm/di, C. 1.5 gm/ dl, D. 12 gm/dl', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. 1.5 01', 'role': 'assistant'}]