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

A

directly proportional to $$R$$ but inversely proportional to $$v$$.

B

directly proportional to both radius $$R$$ and velocity $$v$$.

C

inversely proportional to both radius $$R$$ and velocity $$v$$.

D

inversely proportional to $$R$$ but directly proportional to velocity $$v$$.