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': 'All the following are passive tooth borne functional\nappliances except \nSelect and explain. \nA. Andersen activator, B. Woodside and Hawley activator, C. Expansion activator, D. Herbst appliance', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]