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 most frequent cause of fracture of a root tip\nduring extraction of a primary molar is \nSelect and explain. \nA. Ankylosis of the tooth, B. Improper use of cow horn forceps, C. Presence of supernumerary premolar, D. Root resorption between apex and bifurcation', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]