For solid spheres falling vertically downwards under gravity in viscous fluid, the terminal velocity, V varies with diameter D of the sphere as
(a) $V\alpha D^{\frac{1}{2}}$ for all diameter
(b) $V\alpha D^{2}$ for all diameters
(c) $V\alpha D^{2}$ for large D and $V\alpha D^{2}$ for
small D
(d) $V\alpha D^{2}$ for large D and $V\alpha D^{\frac{1}{2}}$ for
small D