Ans: A. 5 times. Poiseuille's law:* Also referred as "Hagen-Poiseuille law".* Poiseuille's equation states, - Q = P1 - P2 * { (P r4) / (8 e L)} - Q - Flow rate - (P1 - P2) - Pressure difference across vessel (provided P1 > P2). - e - Blood viscosity. - r - Radius. - L - Tube length.* If parameter values remain constant, - Blood flow is directly propoional to 4th power of radius.* Resistance of vessel to blood flow can be calculated by combining Ohm's law with Poiseuille's equation. - By substituting values of Q from Poiseuille's law in Ohm's law. - Implying, resistance is mainly affected by, 1. Blood vessel radius, 2. Vasodilatation/vasoconstriction.* Thus ultimately, if parameter values remain constant, - Resistance to blood flow is inversely propoional to the 4th power of radius.