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: Radiology
Which among the following are a cause of posterior mediastinal opacity on Posterior-Anterior (PA) and lateral view of chest radiograph? 
Select and explain. 
A. Tortuous innominate artery, B. Bochdalek's Hernia, C. Enlarged pulmonary artery, D. Thymoma
B: Bochdalek's Hernia
Answer: B: Bochdalek's Hernia 
Explanation: Amongst the given options Bochdalek hernia is the posterior mediastinal mass.
Tortuous innominate artery and enlarged pulmonary artery (e.g. aneurysm) are middle mediastinal mass, and thymoma is anterior mediastinal mass.