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': 'NOT a content of middle mediastinum: \nSelect and explain. \nA. Ascending aoa, B. Oesophagus, C. Pulmonary trunk, D. Phrenic nerve', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The esophagus is considered to be located in the superior and posterior mediastinum.', 'role': 'assistant'}]