This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Retina, Subject name: Ophthalmology
[{'content': 'Calcification is seen in all of the following except: \nSelect and explain. \nA. Persistent hyperplastic primary vitreous, B. Retinoblastoma, C. Choroidal osteoma, D. Optic nerve head drusen', 'role': 'user'}, {'content': 'Answer: A \nExplanation: All of the following have characteristic calcification as a sign of identification except persistent hyperplastic primary vitreous. Ocular Structures that can have Calcification Concretions In conjunctiva Optic nerve head drusen Retinoblastoma Choroidal Osteoma Pthisical eyeball Band shaped keratopathy', 'role': 'assistant'}]