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: Physiology
Reynolds number describes the relationship between all of the following, EXCEPT: 
Select and explain. 
A. Viscosity of fluid, B. Density of fluid, C. Velocity of flow, D. Direction of flow
D: Direction of flow
Answer: D: Direction of flow 
Explanation: Reynolds number (Re) gives a measure of the ratio of ineial forces to viscous forces. Describes the relation between density of the fluid, diameter of the tube, velocity of flow and viscosity of fluid. The higher the value of Re greater the probability of turbulence. When Re is less than 2000 flow is usually not turbulent. When Re is more than 3000 flow is always turbulent.Re = r x V x D ..............u Ref: Ganong's Review of Medical Physiology, 21st Edition, Page 585