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: Ophthalmology
[{'content': 'Retinoblastoma is bilateral in: \nSelect and explain. \nA. 1% of cases, B. 50% of cases, C. 100% of cases, D. 30% of cases', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. 30% of cases', 'role': 'assistant'}]