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
[{'content': 'Prophylactic therapy should be started against Pneumocystis carinii pneumonia in AIDS patients with CD4 counts below : \nSelect and explain. \nA. < 50/microL, B. < 150/ microL, C. < 200/ microL, D. < 400/ microL', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]