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
To avoid external transportation of the root canal 
Select and explain. 
A. precurve instruments., B. use large instruments., C. avoid the use of sodium hypochlorite., D. use vigorous instrumentation.
A: precurve instruments.
Answer: A: precurve instruments. 
Explanation: None