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': 'Only cataract which is reversible on treatment \nSelect and explain. \nA. Diabetic cataract, B. Oil drop cataract, C. Chalcosis, D. Shield cataract', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Only cataract which is preventable/reversible on treatment\xa0Oil drop cataract.', 'role': 'assistant'}]