This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Ophthalmology
[{'content': 'What percent of retinoblastomas are Bilateral? \nSelect and explain. \nA. 10, B. 20, C. 30, D. 50', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Retinoblastoma is the most common primary malignant intraocular tumor in children, occurring in approximately one of 20000 bihs. In 30% of all cases, it is bilateral.', 'role': 'assistant'}]