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: Pathology
Which is the most common site for peptic ulcer disease ? 
Select and explain. 
A. Second portion of Duodenum, B. Proximal stomach, C. Distal stomach, D. First portion of duodenum
D: First portion of duodenum
Answer: D: First portion of duodenum 
Explanation: First portion of duodenum is the most common site for PUD.