This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hyper Pigmented Disorders, Subject name: Dental
[{'content': 'Which is the most effective topically applied bleaching agent? \nSelect and explain. \nA. Tretinoin, B. Hydroquinone, C. Salicylic acid, D. Toc', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hydroquinone is most effective topically applied bleaching agent. It bleach freckles and lentigens but not cafe-au-lait spots or pigmented nevi.', 'role': 'assistant'}]