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: Psychiatry
[{'content': "Reversible cause of dementia -a) Hypothyroidismb) Alzheimer's diseasec) Vitamin B12 deficiencyd)  Vitamin A deficiency \nSelect and explain. \nA. ac, B. bc, C. ad, D. b", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]