Tide is the regular rise and fall of the ocean level caused by the movement of the sun， the earth and the moon． It is considered a promising source of green energy to produce electricity in coastal areas．

    To make use of tidal energy， we need to build tidal power stations． The bays and the river mouths where the tide is high（the tidal range is more than 10 metres） are usually perfect sites to build tidal power stations． There are many such places in the world． According to the IRENA （ the International Renewable Energy Agency）， by just using 2% of our coastlines， we can produce 4，383TWh of ocean power each year， enough to meet 16.4% of the world's electricity needs．

    To build a tidal power station， we need to build a dam． In the dam are many turbines and on each turbine there is an electric generator'． When the tide rises，water comes through the dam，the turbines turn and the electric generators work， producing electricity．When the tide falls，water goes out through the dam， the turbines turn again．The electric generators continue to work．

    Tidal energy has its advantages．Using tidal energy to produce electricity is much cheaper than using the traditional energy， like coal or gas． For example， the Rance Tidal Power Station in France has been there for over 50 years， producing around 5.000.000TWh of electricity each year． The cost is only 1.3 cents/TWh．

    Tidal energy can be used nearly 24 hours a day． As long as the sun， the earth and the moon exist，we can use it to produce electricity． But without sunshine， there is no solar energy． When there is no wind，electric generators will not work． In addition， with the development of modern technology， tidal energy can be stored and used to produce electricity continuously．

    However， we still have some problems to solve． It is difficult to build a dam in the sea， and the cost is very high．Moreover it's expensive to keep a tidal power station in its best condition．Scientists are working on them．

（1）A tidal power station is best built 　　．

A．at a river mouth with wind

B． along the coast with waves

C． In a bay with tide high enough

D．in coastal areas with sunshine

（2）The underlined word "turbine" in Paragraph Three is a machine to 　　．

A． make the tide rise and fall

B． make an electric generator work

C． let water go through the dam

D．keep the dam in good condition

（3）What advantage does tidal energy have？　　

A． We can use it to get useful tide．

B． It can improve the ocean environment．

C． We can use it nearly all the time．

D． It meets 16． 4% of the electricity needs．

（4）How can we make better use of tidal energy？　　

A． By digging more bays and river mouths．

B． By building cheaper tidal power stations．

C． By closing traditional electric power plants．

D． By using tidal energy to replace other energy．