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
Adenocarcinonia in oesophagous occurs in - 
Select and explain. 
A. Middle esophagus, B. Upper esophagus, C. Barret's ulcer, D. None of the above
C: Barret's ulcer
Answer: C: Barret's ulcer 
Explanation: None