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': 'Loss of cardiac silhoutee is seen in pathology of: \nSelect and explain. \nA. Rt. Middle lobe, B. Rt. Lower lobe, C. Rt. Atria, D. Rt. Ventricle', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. Rt. Middle lobe', 'role': 'assistant'}]