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
Which of the following is a retroperitoneal structure? 
Select and explain. 
A. Ileum, B. Jejunum, C. Ureter, D. Appendix
C: Ureter
Answer: C: Ureter 
Explanation: Ureter