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
If the radius of dentinal tubule is halved, the flow rate will decrease by: 
Select and explain. 
A. 2 times, B. 4 times, C. 8 times, D. 16 times
D: 16 times
Answer: D: 16 times 
Explanation: Flow rate is a function of tubule diameter,pulpal pressure difference,viscosity and tubule length. 
A two fold reduction which means making it half, results in a 16 fold reduction as per the formula.