This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: mycology, Subject name: Microbiology
[{'content': 'Pneumocystis carinii causes primary infection in \nSelect and explain. \nA. Rats, B. Mice, C. Humans, D. Rabbits', 'role': 'user'}, {'content': 'Answer: A \nExplanation: There are two known species of Pneumocystis - Pneumocystis carinii, commonly found in rats and Pneumocystis jirovecii seen in humans. Ref: Textbook of Microbiology, Ananthanarayan and Paniker; 9th edition', 'role': 'assistant'}]