This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Surfaces and Grooves, Subject name: Anatomy
[{'content': 'Which of the following forms Anterior boundary of Middle mediastinum? \nSelect and explain. \nA. Sterno-pericardial ligaments, B. Oesophagus, C. Azygos vein, D. Descending thoracic aoa', 'role': 'user'}, {'content': 'Answer: A \nExplanation: BOUNDARIES OF MIDDLE MEDIASTINUM: Anteriorly - sterno-pericardial ligaments Posteriorly - esophagus, descending thoracic aoa, Azygos vein On each side - Mediastinal pleura', 'role': 'assistant'}]