Consider steady, laminar, fully developed flow of an incompressible Newtonian fluid through two horizontal straight pipes, $I$ and $II$, of circular cross section. The volumetric flow rates in both the pipes are the same. The diameter of pipe $II$ is twice the diameter of pipe $I$, i.e., $d_{II}=2d_I$. The ratio of the shear stress at the wall of pipe $I$ to the shear stress at the wall of pipe $II$ is

1. $0.5$
2. $2$
3. $4$
4. $8$