共用题干

共用题干
Renewable Energy Sources
Today petroleum provides around 40%of the world's energy needs,mostly fuelling automobiles .Coal is still used,mostly in power stations,to cover one-quarter of our energy needs,but it is the least efficient,unhealthiest and most environmentally damaging fossil fuel.Natural gas reserves could plug some of the gap from oil,but reserves of that will not last into the 22nd century either.
Most experts predict we will exhaust easily accessible reserves within 50 years.We could fasi reach an energy crisis.We need to rapidly develop sustainable solutions to fuel our future.Lesspolluting renewable energy sources offer a more practical long-term energy solution.They may benefit the world's poor too."Renewable"refers to the fact that these resources are not used faster than they can be replaced.
The Chinese and Romans used watermills over 2,000 years ago. But the first hydroelectric dam was built in England in 1870.Hydroelectric power is now the most common form of renewable energy,supplying around 20%of world electricity. China's Three Gorges Dam,which has just been completed,is the largest ever. At five times the size of the US's Hoover Dam,its 26 turbines will generate the equivalent energy of 1 8 coal-fired power stations.It will satisfy 3%of China's entire electricity demand.Surprisingly,some argue that hydroelectric dams significantly contribute green- house gases.
In 2003,the first commercial power station to harness tidal currents in the open sea opened in Norway .It is designed like windmill,but others take the form of turbines.
As prices fall,wind power has become the fastest growing type of electricity generation-quadrupling worldwide between 1999 and 2005 .Modern wind farms consist of turbines that gener- ate electricity.Though it will be more expensive,there is more than enough wind to provide the world's entire energy needs. Wind farms come in onshore and offshore forms.They can often end up at spots of natural beauty,and are often unpopular with residents.And turbines are not totally benignthey can interfere with radar and leave a significant ecological footprint,altering climate and killing sea birds.Migrating birds may have more luck avoiding them.Scotland is building
Europe's largest wind farm,which will power 200,000 homes.The UK's goal is to generate one- fifth of power from renewable sources,mainly wind,by 2020 .But this may cause problems,be- cause wind is unreliable.

China's Three Gorges Dam______.
A: is the first hydroelectric dam in the world
B: is of the same size of the US's Hoover Dam
C: is the largest of all the hydroelectric dams in the world
D: supplies around 20%of the world electricity