A 6-m-diameter spherical tank is filled with liquid oxygen (r = 1141 kg/m³, cp = 1.71 kJ/kg·°C) at 2184°C. It is observed that the temperature of oxygen increases to 2183°C in a 144-hour period. The average rate of heat transfer to the tank is
(a) 249 W

(b) 426 W

(c) 570 W

(d) 1640 W

(e) 2207 W