This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Medicine
[{'content': "A patient aged 50 years, with Down's syndrome, presents with difficulty in speech, what is the diagnosis? \nSelect and explain. \nA. Cerebrovascular accident, B. Lacunar infarct in cerebellum, C. Senile dementia Alzheimer's type, D. Alzheimer with prion", 'role': 'user'}, {'content': "Answer: C \nExplanation: (C) Senile dementia Alzheimer's type", 'role': 'assistant'}]