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
Most commonly used technique for determination of working length of a 8 year old  child patient of teeth maxillary central incisor: 
Select and explain. 
A. Tactile sensation, B. Moisture on paperpoint, C. Digital, D. None
B: Moisture on paperpoint
Answer: B: Moisture on paperpoint 
Explanation: As 8 year old patient has central incisor with open apex, hence paper points are most commonly used method.