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': 'A "Vascular Ring" causing external airway compression can be diagnosed by: \nSelect and explain. \nA. CT, B. PET CT, C. MRI, D. Angiography of aoic and pulmonary circulation', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Angiography of aoic and pulmonary circulation', 'role': 'assistant'}]