Five spheres are falling through the same viscous fluid, not necessarily at their terminal speeds. The radii r and speeds v of the spheres are given. Rank the spheres in order of decreasing viscous drag force on them.

(a) r= 1.0 mm, v = 15 mm/s (b) r= 1.0 mm, v = 30 mm/s (c) r= 2.0 mm, v = 15 mm/s (d) r= 2.0 mm, v = 30 mm/s (e) r= 3.0 mm, v = 20 mm/s