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': "Most common cause of dementia is : \nSelect and explain. \nA. Vitamin B12, B. Parkinsonism, C. Alzheimer's disease, D. Road traffic accidents", 'role': 'user'}, {'content': "Answer: C \nExplanation: Alzheimer's disease is the most common cause of dementia.", 'role': 'assistant'}]