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': 'Central cyanosis is seen if \nSelect and explain. \nA. Methemoglobin 0.5 gm/dl, B. O2 saturation < 85%, C. O2 saturation < 94%, D. Hb – 4 gm%', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Oxygen saturation should be less than 85% for central cyanosis to occur. Deoxyhemoglobin level should be at least 5gm%.', 'role': 'assistant'}]