Spherical balls of radius R are falling in a viscous fluid of viscosity Ƞ 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