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: Microbiology
[{'content': 'An 66--year--old AIDS patient with pneumonia has a bronchoalveolar lavage that demonstrates small, "hat-shaped" structures in alveoli that are about the size of an erythrocyte and stain with silver stains. The microorganism involved is most likely which of the following? \nSelect and explain. \nA. Blastomyces dermatitidis, B. Mycobacterium a vium, C. Mycobacterium tuberculosis, D. Pneumocystis carinii', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Pneumocystis carinii', 'role': 'assistant'}]