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
In an AIDS patient presenting with a fever cough, a diagnosis of pneumocystis carinii pneumonia is best established by- 
Select and explain. 
A. Transtracheal biopsy, B. Broncho alveolar lavage, C. Staining of intranuclear inclusion and silver staining, D. Aspiration and culture
B: Broncho alveolar lavage
Answer: B: Broncho alveolar lavage 
Explanation: None