This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: G.I.T, Subject name: Surgery
Which of the following organs is the most common site of origin of the tumour associated with the Zollinger-Ellison syndrome 
Select and explain. 
A. Duodenum, B. Lymph nodes, C. Spleen, D. Pancreas
A: Duodenum
Answer: A: Duodenum 
Explanation: Gastrin producing endocrine tumour is often found in the duodenal loop,although it also occurs in the pancreas,especially in the head. Bailey & Love ,26th, 1055.