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': 'Which antiglaucoma drug decreases aqueous formation ? \nSelect and explain. \nA. Prostaglandins, B. Beta - blockers, C. Mannitol, D. Pilocarpine', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Beta - blockers", 'role': 'assistant'}]