The figure shows the tungsten filament of a bulb with constant diameter except a piece of it which has half the diameter of the rest of the wire. Assume that the temperature is constant within each part and changes suddenly between the parts. If the temperature of thick part is 2000 K, the temperature of the thin part of the filament is
(A) 2000 K
(B) 21/4(2000) K
(C) 81/4|(2000) K
(D) 41/2(2000) K
