A small steel ball of mass `m` and radius `r` is falling under gravity through a viscous liquid of coefficient of viscosity `eta`. If `g` is the value of acceleration due to gravity. Then the terminal velocity of the ball is proportional to (ignore buoyancy)
A. `(mg eta)/(r)`
B. `mg etar`
C. `(mgr)/(eta)`
D. `(mg)/(reta)`
