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
Impedence based apex locator is: 
Select and explain. 
A. Generation 1, B. Generation 2, C. Generation 3, D. Generation 4
B: Generation 2
Answer: B: Generation 2 
Explanation: Second Generation Apex Locator (Impedance-based Apex Locator) / Low Frequency Apex Locator

Inoue introduced the concept of impedance-based apex locator which measures opposition to flow of alternating current or impedance.
This apex locator indicates the apex when two impedance values approach each other.