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. Caecum, B. Transverse colon, C. Descending colon, D. Sigmoid colon', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Descending colon', 'role': 'assistant'}]