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
Fluid flow in and out of the dentinal tubules is proportional to the tubule diameter by: 
Select and explain. 
A. Third power of the diameter, B. Sixth power of the diameter, C. Square of diameter, D. Fourth power of diameter
D: Fourth power of diameter
Answer: D: Fourth power of diameter 
Explanation: Fluid flow in dentin tubules follows Poiseuille’s law as all tubular structures: