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: Dental
[{'content': 'The technique of home bleaching prescribed by dentist \nSelect and explain. \nA. Walking bleach, B. Night guard, C. Both, D. None.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Although a 3% ether and peroxide mouthwash used for bleaching in 1893 has been reported in the literature, the “dentist-prescribed, home-applied” technique (also referred to as nightguard vital bleaching or at-home bleaching) for bleaching vital teeth outside the oice began around 1968, although it was not commonly known until the late 1980s.\nWalking bleach is a non vital bleaching procedure.', 'role': 'assistant'}]