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': 'What is the most common opportunistic infection in AIDS? \nSelect and explain. \nA. Tuberculosis, B. Cryptococcosis, C. Pneumocystitis carinii, D. Histoplasmosis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]