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': 'After enamel has been exposed to bacteria, irreversible bacterial colonization takes place in about \nSelect and explain. \nA. 24 hrs, B. Few minutes, C. 1-2 hrs, D. 2-4 hrs', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]