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': 'Endocater is: \nSelect and explain. \nA. 1st generation apex locator., B. 2nd generation apex locator., C. 3rd generation apex locator., D. 4th generation apex locator.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: APEX Locators:', 'role': 'assistant'}]