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 burrowing ulcer is caused by? \nSelect and explain. \nA. Microaerophilic streptococci, B. Peptostreptococcus, C. Streptococcus viridians, D. Streptococcus pyogenes', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]