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: Surgery
[{'content': 'Chronic thick walled pyogenic abscess may be due to the following except \nSelect and explain. \nA. Presence of a foreign body, B. Prolonged antibiotic therapy, C. Virulent strains of organism, D. Inadequate drainage', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]