A 2-in. diameter shaft is supported by two sleeves, each of length = 2 in. The internal diameter of the sleeves is 2.1 in. The radial space between the shaft and the sleeves is filled with an oil of viscosity = 8 × 10-3 lb-s/ft2. If the shaft is rotated at a speed of 600 rpm, the viscous torque (ft-lb) on the shaft is most nearly （ ）。 A. 0.15 B. 0.64 C. 3.20 D. 6.40