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': 'Which is not an indication for walking bleach: \nSelect and explain. \nA. Discolouration of the pulp chamber., B. Defective enamel formation., C. Dentin discolouration., D. None.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]