Energy is used for heating a building by a heating system.
Solar energy is the energy in the sun's rays.
The sun's rays can be used for heating a building by a heating system.
What can be used for heating a building by a heating system?
a: the Sun's rays
b: peachleaf willow
c: engines
d: oxygen
e: photosynthesis
f: photons
g: air
h: hydrogen and oxygen