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 burrowing ulcer is caused by? 
Select and explain. 
A. Microaerophilic streptococci, B. Peptostreptococcus, C. Streptococcus viridians, D. Streptococcus pyogenes
A: Microaerophilic streptococci
Answer: A: Microaerophilic streptococci 
Explanation: None