Energy is used for heating a building by a heating system.
Faculty offices are also in the building.
Energy used to heat an office is by a heating system.
What contains energy to raise the temperture of an office?

[1] chemical messengers
[2] peachleaf willow
[3] deoxyribonucleic acid
[4] cooling system
[5] swimming pool
[6] heating system
[7] gym
[8] organic molecules