This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Microbiology
Poiseuille's Hagen law is 
Select and explain. 
A. F = (PA-PB) X 3.14 X r^4/8nl, B. F = (PA+PB) X 3.14 X r^4/8nl, C. F = (PA/PB) X 3.14 X r^4/8nl, D. F = (PA X PB) X 3.14 X r^4/8nl
A: F = (PA-PB) X 3.14 X r^4/8nl
Answer: A: F = (PA-PB) X 3.14 X r^4/8nl 
Explanation: Poiseuille-Hagen FormulaThe relation between the flow in a long narrow tube, the viscosity of the fluid, and the radius of the tube is expressed mathematically in the Poiseuille-Hagen formula:F = (PA-PB) X (dj/8) X (1/dj) X (r4/L)whereF = FlowPA-PB = Pressure difference between the two ends of the tubedj = Viscosityr = Radius of tubeL = Length of tube