This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Tumors, Subject name: Ophthalmology
[{'content': "Knudson's two stage hypothesis is for- \nSelect and explain. \nA. Glaucoma, B. Retinoblastoma, C. Optic glioma, D. Meningioma", 'role': 'user'}, {'content': "Answer: B \nExplanation: *Deletion or inactivation of RB gene by two mutations (knudson's two hit hypothesis) results in occurence of retinoblastoma. Ref: Khurana 7th/e p.314.", 'role': 'assistant'}]