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': 'Fourth generation of apex locator are based on which principle \nSelect and explain. \nA. Resistance based, B. Impedance based, C. Impedance ratio based, D. Multiple frequencies based', 'role': 'user'}, {'content': 'Answer: D \nExplanation: First generation …resistance based\nSecond…impedence\nThird…impedence ratio\nFourth ..multifrequency', 'role': 'assistant'}]