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': 'Early change of pulmonary edema in CXR: \nSelect and explain. \nA. Batswing appearance, B. Pleural effusion, C. Kerley B lines, D. Ground gram lung field', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Kerley B lines', 'role': 'assistant'}]