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
A patient report to the dentist with trauma to immature tooth with open apex now dentist plan to do R.C.T. Best way to measure working length in this patient is by ? 
Select and explain. 
A. Electronic apex locator, B. Radiographic method, C. Tactile method, D. Paper point
D: Paper point
Answer: D: Paper point 
Explanation: None