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: Anatomy
[{'content': 'Which of the following is a retroperitoneal structure? \nSelect and explain. \nA. Ileum, B. Jejunum, C. Ureter, D. Appendix', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ureter', 'role': 'assistant'}]