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': 'Instrument used for gingival retraction during rubber\ndam placement is \nSelect and explain. \nA. retainer no:208, B. retainer no:210, C. retainer no:212, D. retainer no:216', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]