At present , most of our energy comes from fossil fuels (oil , coal , and natural gas). However , such reserves are limited . Because power demand is increasing very rapidly , fossil fuels will be exhausted within a relatively short time . Therefore , people must develop and use alternative sources of energy.
One alternative source is nuclear energy . Nuclear energy can provide enough electricity for the world`s needs for hundreds of years , but it can be very dangerous . Another alternative source of energy is geothermal heat , which comes from deep inside the earth . Scientists use this heat to make energy . However , this energy is available only in a few places in the world.
The sun , water , and the wind are other alternative sources of energy . The wind turns windmills and moves sailboats . It is a clean source of energy , and there is lots of it . Unfortunately , If the wind does not blow , there is no wind energy . When water moves from a high place to the lower place , it makes energy . And as dams cost a lot of money , so water energy is expensive.
The sun releases large amounts of energy every day . This energy can be changed into electricity . Many countries use solar energy for their daily life . Solar panels on the roofs of houses can create enough energy to heat or cool an entire house . Solar energy is not only plentiful and infinite but also clean and safe.
Although there are some disadvantages , the potential of alternative sources of energy is great . However , how to make full use of these sources of energy is a question for researchers all over the world.

Read the passage and then do the tasks that follow
While you read
1 . Six hundred balloons were ______________ at the ceremony .
2 . They are looking for _______________ methods of making it .
3 . People use ________________ to run machines , heat and cool their homes .
4 . The food in the restaurant is cheap , but the choice
is rather_________________ .
5 . Fuel supplies are nearly_________________ .
Complete the summary of the reading passage by filling each blank with a suitable word from the box
We need energy to live and work.Our nature source of (1) ______is oil . Oil is (2)____ kind of fossil fuel. The amount of fossil (3)_____ in the world is(4) _____ . Therefore, we must save it, and at the same time, we must fine new source of energy. Geothermal heat and nuclear power are (5)__________ source of energy. They can give us electricity. Other alternative (6) _______ are the sun, waves and water. These source are not only (7)________ and available but also clean and save for the (8)_________ . People should develope and use them more and more in the future.