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
All the following are passive tooth borne functional
appliances except 
Select and explain. 
A. Andersen activator, B. Woodside and Hawley activator, C. Expansion activator, D. Herbst appliance
C: Expansion activator
Answer: C: Expansion activator 
Explanation: None