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': 'Pit & tissue sealants act by \nSelect and explain. \nA. Killing micro-organism causing caries, B. Blocking nutrient supply to bacteria, C. Neutralising acid produced by bacteria, D. All of these', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]