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
[{'content': 'Posterior marking on Ba column in Ba swallow study is caused by? \nSelect and explain. \nA. Aoic knuckle, B. Left atrium, C. Aberrant right subclan aery, D. Pulmonary aery sling', 'role': 'user'}, {'content': 'Answer: C \nExplanation: C i.e. Aberrant right subclan aery An aberrant right subclan aery arises from the aoic arch distal to the origin of left subclan aery, and passes upwards & to the right behind the oesophagus. This gives rise to a classical smooth, oblique indentation on posterior wall of barium filled oesophagusQ.', 'role': 'assistant'}]