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': 'Root of mesentery is crossed by - \nSelect and explain. \nA. Horizontal part of duodenum, B. Left gonadal vessels, C. Left ureter, D. Superior mesenteric artery', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]