Spherical balls of radius R are falling in a viscous fliud of viscosity $\eta$ with a velocity v. The retarding viscous force acting on the spherical ball is

Question

( A ) inversely proportional to both radius R and velocity v
( B ) directly proportional to R but inversely proportional to v.
( C ) inversely proportional to R but directly proportional to velocity v.
( D ) directly proportional to both radius R and velocity v