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 main action of the reciprocating arm is \nSelect and explain. \nA. Reciprocates the action of the retentive arm, B. Reciprocation of vertical displacement, C. To provide stability to the denture, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]