Two small spherical metal balls, having equal masses, are made from materials of densities ${\rho }_1$ and ${\rho }_2$ such that ${\rho }_1=8{\rho }_2$ and having radii of $r_1$ and $r_2$, respectively. They are made to fall vertically (from rest) in a viscous medium whose coefficient of viscosity equals $\eta$ and whose density is $0.1{\rho }_2$. The ratio of their terminal velocities would be:

1. A
   $\frac{79}{72}$
2. B
   $\frac{19}{36}$
3. C
   $\frac{39}{72}$
4. D
   $\frac{79}{36}$