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 structures is NOT found in both the superior and posterior mediastinum? \nSelect and explain. \nA. Vagus nerve, B. Esophagus, C. Thoracic duct, D. Trachea', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Since the trachea bifurcates at T4, it is not found in the posterior mediastinum', 'role': 'assistant'}]