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
Endocater is: 
Select and explain. 
A. 1st generation apex locator., B. 2nd generation apex locator., C. 3rd generation apex locator., D. 4th generation apex locator.
B: 2nd generation apex locator.
Answer: B: 2nd generation apex locator. 
Explanation: APEX Locators: