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
Which of the following forms Anterior boundary of Middle mediastinum? 
Select and explain. 
A. Sterno-pericardial ligaments, B. Oesophagus, C. Azygos vein, D. Descending thoracic aoa
A: Sterno-pericardial ligaments
Answer: A: Sterno-pericardial ligaments 
Explanation: BOUNDARIES OF MIDDLE MEDIASTINUM: Anteriorly - sterno-pericardial ligaments Posteriorly - esophagus, descending thoracic aoa, Azygos vein On each side - Mediastinal pleura