Ans: C. Reduce by 1/16Option c is correct because the flow of fluids can be described by Poiseuille's Law.In which flow of liquid is directly proportional to R4, So if lumen is reduced to half then blood flow will get reduce by 1/16.Other points related to blood flow...Poiseuille's Law states that the flow (Q) of fluid is related to a number of factors:The viscosity (n) of the fluidThe pressure gradient across the vessel (P)Length (L) and diameter(r) of the vesselDiameter: Doubling the diameter of tube increases the flow rate by 16 fold (r4). The larger the vessels's diameter greater is the blood flow.Viscosity: Flow is inversely proportional to the viscosity of the fluid.Viscosity of blood increases with increasing hematocrit and decreasing temperaturePressure: Increasing pressure further maximizes flow as described by Poiseuille's equation.The relationship is given by Poiseuille-Hagen formula:F=(PA -PB )x(8p )x(e1 )x(Lr4 )WhereF = FlowPA - PB = Pressure difference between two ends of the tube q = Viscosity r = Radius of tube L = Length of tubeRelationship between arterial blood pressure and blood flow given in graph below: