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
[{'content': 'Calcium is absorbed from: \nSelect and explain. \nA. Duodenum, B. Jejunum, C. Ileum, D. Colon', 'role': 'user'}, {'content': 'Answer: A \nExplanation: All the divalent cations, except Mg++ , are absorbed from duodenum. Mg++ is absorbed from ileum. Calcium is absorbed mainly in duodenum and upper jejunum, not whole of jejunum.', 'role': 'assistant'}]