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 triangular opacity with clear borders, base towards midline and obliterating right heart border on a chest radiograph suggest that the pathology is likely to be in - \nSelect and explain. \nA. Apical segment of right lower lobe, B. Medial segment of right lower lobe, C. Right middle lobe, D. Any of the above', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Right middle lobe pathology obliterates lower right border of heart producing silhouette sign.', 'role': 'assistant'}]