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
A 30-year-old HIV positive patient presents with fever, dyspnoea and non-productive cough. The patient is cyanosed. His chest X-ray reveals bilateral, symmetrical interstitial infiltrates. The most likely diagnosis is - 
Select and explain. 
A. Tuberculosis, B. Cryptococcosis, C. Pneumocystis carinii pneumonia, D. Toxoplasmosis
C: Pneumocystis carinii pneumonia
Answer: C: Pneumocystis carinii pneumonia 
Explanation: None