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 glucose rinse, the duration for which  pH drop is seen in interproximal plaque: \nSelect and explain. \nA. 20 minutes, B. 60 minutes, C. 120 minutes, D. 180 minutes', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]