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': 'The esophagus - \nSelect and explain. \nA. Begins at the upper border of cricoid cartilage, B. Runs a straight course throughout, C. Is narrowest at its termination, D. Is narrowest at its beginning', 'role': 'user'}, {'content': 'Answer: D \nExplanation: At the lower end of pharynx, at the level of lower border of cricoid cartilage, esophagus begins. It is narrowest at its beginning due to cricopharyngeal sphincter. Then it runs a curved route rather than being straight.', 'role': 'assistant'}]