[" Spherical balls of radius "' are falling in a viscous fluid of viscosity' " "with a velocity " "The retarding viscous "],[" force acting on the spherical ball is "],[" (A) Inversely proportional to ' but directly proportional to velocity "v' "],[" (B) Directly proportional to both radius 'r' and velocity 'v' "],[" (C) Inversely proportional to both radius 'r' and velocity 'v' "],[" (D) Directly proportional to ' but inversely proportional to 'v' "]