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
On barium swallow posterior indentation is seen due to: 
Select and explain. 
A. Left atrium, B. Aoic knuckle, C. Aberrant right subclan, D. Sling of pulmonary aery
C: Aberrant right subclan
Answer: C: Aberrant right subclan 
Explanation: Ans. Aberrant right subclan