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': 'Age related dementia has been associated with increased levels of- \nSelect and explain. \nA. Homocysteine, B. Cysteine, C. Tourine, D. Methionine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]