A common argument for expanding renewable energy sources is that technologies such as solar panels （太阳板）release far less carbon dioxide than power plants（发电厂） that burn oil．
Only about 3 percent of the Earth's water is freshwater， most of which is frozen-That means only 0.8 percent of the planet's water can be served for human use． Water is a necessary， but limited product． And nearly 1 billion people worldwide lack of fresh water． In the U．S．， 45.3 percent of the freshwater is used to cool off thermoelectric （热电）power plants： nuclear reactors and plants that burn oil．
To provide electricity for an average home， a nuclear power plant requires 615 gallons of cooling water a day， a coal-fired plant， 199 gallons per day， and a natural gas power plant， 114 gallons per day． Let's look at how much water each power source takes to make one megawatt（兆瓦）-hour of electricity．
Nuclear reactors are the highest， at 13，000 gallons． Then comes coal， natural gas． The water needed by solar panels is lower． These numbers only reflect operations to make electricity； they do not include water used to get the fuel or make the power． For example， fracking （水力压裂）can use hundreds of thousands of gallons each time to make a rock cracked to release natural gas． Large quantities of water becomes vapor． The rest is sent back to the environment， but some of that is fixed with chemicals， and most of it is hot， which can kill fish and other living things．
Natural gas， coal and nuclear power plants ranked one， two and three in 2016， according to the total amount of U．S． electricity made in a year． And natural gas is projected to become even more important through 2050．
To protect fresh water， it seems clear that the country should change toward renewables． This would make more freshwater for food production and human use．



Which uses the most water to make electricity？ ______

A. Coal-fired plant．
B. A natural gas power plant．
C. Solar panels．
D. A nuclear power plant．

For what purpose does the author provide so many numbers？ ______

A. To provide proof to scientists．
B. To state the fact of making electricity．
C. To tell readers to treasure freshwater．
D. To prove that non-renewable energy uses much more water．

What suggestion does the author make in the passage？ ______

A. Fresh water should be protected．
B. Renewable energy should be put into use．
C. Non-renewable energy should use less water．
D. People should save fresh water．

What is the main idea of the text？ ______

A. Non-renewable energy pollutes environment．
B. Renewable energy saves water．
C. Electricity needs much water to make．
D. Ways are listed to make electricity．