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': 'pH and duration of Action of EDTA is \nSelect and explain. \nA. 7.2-7.3 and 15 min, B. 6.8-6.9 and 12 min, C. 7.2-7.3 and 12 min, D. 6.8-6.9 and 15 min', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]