1, Coal is more expensive and more polluting than natural gas.
2, We are looking for cheap and clean, and effective sources of energy.
3, Will fossil fuels be replaced with solar and wind within 20 years?
4, I have visited Yaly hydroelectric power plant once before.
5, The first hydroelectric power plant was built at Niagara Falls in 1979.
6, You should switch off electrical appliances when they are not in use.
7, Despite being the most polluting of fossil fuels, coal is still the largest source of energy worldwide.
8, People will use biogas for fuel in homes and for transport.
