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: Medicine
[{'content': 'Which among the following is not a cause for cyanosis? \nSelect and explain. \nA. Methemoglobin, B. Sulfhemoglobin, C. Cirrhosis, D. Carboxyhemoglobin', 'role': 'user'}, {'content': "Answer: D \nExplanation: Cyanosis is caused by reduced hemoglobin. CO poisoning doesn't cause cyanosis. Approximately 5 g/dL of unoxygenated hemoglobin in the capillaries generates the dark blue color appreciated clinically as cyanosis. Causes: Central Nervous System: Intracranial hemorrhage, Cerebral anoxia Respiratory System: Pulmonary Hypeension, Pulmonary embolism, Hypoventilation, COPD Cardiac Disorders: Congenital hea disease, Hea failure, Hea valve disease Blood: Methemoglobinemia, Polycythaemia Others: High altitude, Hypothermia, Congenital cyanosis (HbM Boston), Obstructive sleep apnea", 'role': 'assistant'}]