Q: Fact 1: Energy is used for heating a building by a heating system. Fact 2: Heating system is Gas. Given the two facts above, what energy is used for heating a building?

Select from:
a). fire.
b). flow of protons.
c). wind.
d). HPV.
e). oil.
f). h2o condensation.
g). thermometers.
h). gas.
The answer is:
h).