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': 'Visual prognosis is poor in: \nSelect and explain. \nA. Bilateral congenital cataract, B. Unilateral congenital cataract, C. Zonular cataract, D. Cataract pulverulenta', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. Unilateral congenital cataract', 'role': 'assistant'}]