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: Skin
Mycobacterium causeing skin ulcer: 
Select and explain. 
A. M.smegmatis, B. M.scrofulaceum, C. M.ulcerans, D. M.fouitum
C: M.ulcerans
Answer: C: M.ulcerans 
Explanation: C i.e. M. ulcerans