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': 'Back action clasp is a modification of: \nSelect and explain. \nA. Ring clasp, B. Embrasure clasp, C. Onlay clasp, D. Hairpin clasp', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Back-action clasp\n\nIt is a modification of the ring clasp.\nHere the minor connector is connected to the end of the clasp arm and the occlusal rest is left unsupported.\n\nDisadvantages:\n\nLack of support to the occlusal rest reduces its function.\nIt has both biological and mechanical unsound principles.', 'role': 'assistant'}]