The velocity of a small ball of mass `` M `` and density `` d `` , when dropped in a container filled with glycerine becomes constant after some time. If the density of glycerine is `` \frac{d}{2} `` , then the viscous force acting on the ball will be:
(A) `` \frac{ Mg }{2} ``
(B) `` Mg ``
(C) `` \frac{3}{2} Mg ``
(D) `` 2 Mg ``