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: Pharmacology
Drug of choice for pneumocystis carinii ? 
Select and explain. 
A. Cotrimoxazole, B. Erythromycin, C. Penicillin, D. Metronidazole
A: Cotrimoxazole
Answer: A: Cotrimoxazole 
Explanation: Ans. is 'a' i.e., Cotrimoxazole