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: Radiology
A patient suffering from AIDS presents with a history of dyspnea and non-productive cough x-ray shows bilateral perihilar opacities without pleural effusion and lymphadenopathy. Most probable etiological agent is – 
Select and explain. 
A. Tuberculosis, B. CMV, C. Kaposis sarcoma, D. Pneumocystis carinii
D: Pneumocystis carinii
Answer: D: Pneumocystis carinii 
Explanation: Dyspnea with a nonproductive cough, and bilateral perihilar opacities without pleural effusion and lymphadenopathy, in an AIDS patient suggest the diagnosis of P. Carinii pneumonia.
In TB, cough is productive (with sputum) and there is associated lymphadenopathy. Pleural effusion may also occur.