This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gastrointestinal System, Subject name: Physiology
Iron is actively absorbed mainly in:- 
Select and explain. 
A. Stomach, B. Duodenum, C. Jejunum, D. Ileum
B: Duodenum
Answer: B: Duodenum 
Explanation: Almost all iron absorption occurs in the duodenum.