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': 'Paint brush appearance is a feature of \nSelect and explain. \nA. Hydronephrosis, B. PCKD, C. Medullary sponge kidney, D. Papillary necrosis', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Paint brush appearance - Medullary sponge kidney.\nEgg in CUP appearance\xa0 - Papillary necrosis.', 'role': 'assistant'}]