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 of the following is a cause of reversible dementia? \nSelect and explain. \nA. Subacute combined degeneration., B. Picks disease, C. Creutzfeldt - Jakob disease., D. Alzheimer's disease", 'role': 'user'}, {'content': "Answer: A \nExplanation: Answer is A (Subacute combined degeneration) `Subacute combined degeneration' is caused by vitamin B12 deficiency. Vitamin deficiencies including vitamin B,2 deficiency constitute potentially reversible causes of dementia.", 'role': 'assistant'}]