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
Due to inward or outward movement of dentinal fluid exciting the nerve endings 
Select and explain. 
A. Direct neural stimulation theory, B. Hydrodynamic theory, C. Transduction theory, D. All of the above
B: Hydrodynamic theory
Answer: B: Hydrodynamic theory 
Explanation: None