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': 'Sodium nitrite is used as \nSelect and explain. \nA. Antiplaque agent, B. Antirust agent, C. Desensitising agent, D. Bleaching agent', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]