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
[{'content': 'Which of the following is the single most important predictor of clinical success of a cast post and core? \nSelect and explain. \nA. Amount of remaining coronal tooth structure., B. Post length., C. Post diameter., D. Positive horizontal stop.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The length, canal enlargement, and a finish line for the post are unimportant, if there is no sound remaining coronal tooth structure to get a ferrule of the final restoration.', 'role': 'assistant'}]