In a furnace, the wall thickness is 60 cm and is 100 cm wide by 150 cm height made of material with thermal conductivity 0.4 W/mK. The temperature inside and outside are $$1000^\circ C$$ and $$4^\circ C$$ respectively. The thermal resistance is

A

1 K/W

B

2 K/W

C

18 K/W

D

15 K/W