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': 'The following affects prognosis of periodontal treatment \nSelect and explain. \nA. Short root, long crown, B. Long root, short crown, C. Apical pearls, D. Root concavities', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]