The velocity of a small ball of mass $\mathrm{m}$ and density $\mathrm{d}_{1}$ when dropped in a container filled with glycerine becomes constants after sometime. What is the viscous force acting on the ball ? (density of glycerine is $\mathrm{d}_{2}$ )
(A) $m g\left\{1-\left(d_{1} / d_{2}\right)\right\}$
(B) $m g\left\{1-\left(d_{2} / d_{1}\right)\right\}$
(C) $m g\left\{d_{1} /\left(d_{1}-d_{2}\right)\right\}$
(D) $\operatorname{mg}\left\{\mathrm{d}_{2} /\left(\mathrm{d}_{1}-\mathrm{d}_{2}\right)\right\}$