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Unit 3 READING 1

R ight now, most of our electricity comes from
coal and oil. But coal and oil have two
problems. First, they are dirty sources of energy.
They cause a lot of pollution. Second, they are
limited sources of energy. Our coal and oil may only
last another 50 years. What will we do then?

Scientists are looking for alternative energy
sources. The perfect energy source would be clean
and renewable . That means we could never use it all. (a) A good example of
a clean and renewable energy source is wind power. (b) The wind turns
giant fans, and this makes electricity. (c) It is clean, and we will never run

out of wind. (d) But wind power does not make enough electricity for
the world. We will have to improve our technology or find other sources
of alternative energy.

English Usage

• or We can use ‘or’ when we are mentioning two or more alternatives.
It is better to delay painting if the ground is wet or frosty.
Boys may do some work in the fields or help in the house.

122 Chapter 6 Science & Technology