Marvin and his igloo

Where inside of the igloo should Marvin put his bed in order to stay as warm as possible?

a) In this position, the distance to all the cold walls is at a maximum and therefore the cold should hit Marvin with a delay.

b) In this position, Marvin is surrounded by heated air and can therefore take a temperature advantage.

c) In this position, Marvin is surrounded by naturally warm earth and can therefore take a temperature advantage.

d) It does not matter which position Marvin chooses. He will cool down equally fast and therefore cannot find a comfortable sleeping position.