Which is the best summary of paragraph 3?
a) fossil fuels are dirty and pollute the air and water. most of the world's energy comes from these fuels.
b) the biggest problem of buildings is that they use fuel that is dirty for heating. they need to do something to be more energy efficient.
c) panels that turn energy from the sun into electricity and passive solar heating can stop the burning of fossil fuels which pollute air and water.
d) since fossil fuels are dirty and pollute the air and water, other technologies that pollute less and produce energy have been developed like solar energy and green buildings.