The velocity of small ball of mass `M` and density `d_(1)` when dropped a container filled with glycerine becomes constant after some time. If the density of glycerine is `d_(2)`, the viscous force acting on ball is
A. `mg((d_(1))/(d_(2)))`
B. `mg(1-(d_(2))/(d_(1)))`
C. `mg((d_(1)+d_(2))/(d_(1)))`
D. `mg((d_(1)+d_(2))/(d_(2)))`