There are many problems in our modern world. One very serious problem is energy. We get a

There are many problems in our modern world. One very serious problem is energy. We get a great 【71】 of energy we need from coal, gas, and oil. However, the 【72】 of energy which we use is 【73】 every year, and we only have enough coal, gas, and oil for the next twenty or thirty years. How will we live 【74】 the energy which these things give us？ Scientists are looking for 【75】 to this problem. They are looking for new 【76】 to produce energy. For example, they are working with new ways 【77】 energy from the light and heat of the sun. They are also working with plans which produce energy from 【78】 of the oceans. All of the new methods 【79】 scientists are finding are still very expensive, but perhaps they will help solve our energy problems 【80】 the future.

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A．number

B．group

C．price

D．deal