This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Thorax, Subject name: Anatomy
Posterior mdiastinum provides passage to all structures except 
Select and explain. 
A. Oesophagus, B. Trachea, C. Descending thoracic aoa, D. Azygous vein
B: Trachea
Answer: B: Trachea 
Explanation: Posterior MediastinumBoundariesAnteriorly: (i) Pericardium, (ii) bifurcation of trachea, (iii) pulmonary vessels, and (iv) posterior pa of the upper surface of the diaphragm.Posteriorly: Lower eight thoracic veebrae and intervening discs.On each side: Mediastinal pleura.Contents1. Oesophagus2. Aeries: Descending thoracic aoa and its branches.3. Veins: (i) Azygos vein, (ii) hemiazygos vein, and (iii) accessory hemiazygos vein.4. Nerves: (i) Vagi, and (ii) splanchnic nerves, greater, lesser and least, arising from the lower eight thoracic ganglia of the sympathetic chain.5. Lymph nodes and lymphatics: (i) Posterior mediastinal lymph nodes lying alongside the aoa, and (ii) the thoracic ductRef: BD Chaurasia; Volume 1; 6th edition