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
A 41-year-old male is admitted to the emergency department with complaints of shortness of breath, dizziness, and sharp chest pain. The large arrow in his chest radiograph indicates the region of pathology. What is this structure? 
Select and explain. 
A. Superior vena cava, B. Right ventricle, C. Left ventricle, D. Arch of the aorta
D: Arch of the aorta
Answer: D: Arch of the aorta 
Explanation: (d) Source: GAS 180-185; GA 85-88The normal position of the heart as seen in a plain radiograph has the right border of the heart formed by the superior vena cava, right atrium, and inferior vena cava. The left border is formed by the aortic arch superiorly, left pulmonary artery, left auricle, left ventricle, and the apex of the heart inferolaterally. The area indicated by the arrow is just inferior to the clavicle (on the left side), and this marks the location of the arch of the aorta. The superior vena cava and right ventricle would make up the right border. The pulmonary artery and left ventricle would be more inferior.