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': 'Preservation of cusps and marginal ridges is: \nSelect and explain. \nA. Primary resistance form., B. Primary retention form., C. Convenience form., D. Secondary retention form.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Features of primary resistance form are:\n\nBox shape.\nFlat floor.\nPreservation of cusps and marginal ridges.\nRounded internal and external line angles.', 'role': 'assistant'}]