In arc welding of butt joint, the welding speed is to be selected such that highest cooling rate is achieved. Melting efficiency and heat transfer efficiency ae 0.5 and 0.7, respectively. The area of the weld cross section is 5 mm2 and the unit energy required to melt the metal is 10 J/mm3. If the welding power is 2 kW, the welding speed in mm/s is closet to
(a) 4 (b) 14 (c) 24 (d) 34