`⇒`
`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 by solar and wind within 20 years.
`4.` I have visited Yaly hydroelectric power plant twice.
`5.` The first hydroelectric power plant was built at Niagara Falls in 1879.
`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.
