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': 'Ferrule is a feature of: \nSelect and explain. \nA. Retention form, B. Resistance form, C. Conservation of tooth structure, D. Antirotational design', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Although there is evidence that preserving as much coronal tooth structure as possible will enhance prognosis, it is less clear whether the prognosis will improve by creating a ferrule in an extensively damaged tooth by surgical crown-lengthening. In this latter circumstance, although the crown-lengthening allows a ferrule, it also leads to a much less favorable crown to root ratio and therefore increased leverage on the root during function.', 'role': 'assistant'}]