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
Chronic thick walled pyogenic abscess may be due to the following except 
Select and explain. 
A. Presence of a foreign body, B. Prolonged antibiotic therapy, C. Virulent strains of organism, D. Inadequate drainage
C: Virulent strains of organism
Answer: C: Virulent strains of organism 
Explanation: None