Please answer the following question: Fact 1: Energy is used for heating a building by a heating system. Fact 2: Solar energy is the energy in the sun's rays. Given the two facts above, answer the question "What can be used for heating a building by a heating system?" with the following options: - the Sun's rays - peachleaf willow - engines - oxygen - photosynthesis - photons - air - hydrogen and oxygen
A:
the Sun's rays