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 vaccine is not useful in a patient with AIDS \nSelect and explain. \nA. OPV, B. P T, C. BCG, D. Measles', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]