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
The success of a root canal filling is best assessed 
Select and explain. 
A. Clinical observation, B. Size of gutta-percha cone used, C. Radiographs, D. By the diameter of root canal reamer
A: Clinical observation
Answer: A: Clinical observation 
Explanation: None