单选题
In search of other energy alternatives, the United
States has been developing its synfuels industry, which is the production of
synthetic fuels to{{U}} {{U}} 1 {{/U}} {{/U}}the place of oil,
coal, and natural gas. One of the new technological processes{{U}} {{U}}
2 {{/U}} {{/U}}with the production of gasohol, a{{U}} {{U}}
3 {{/U}} {{/U}}of 90 percent gasoline and 10 percent alcohol. There are
two types of alcohol used as fuels: ethanol, produced{{U}} {{U}} 4
{{/U}} {{/U}}corn and other grains, and methanol, produced from coal and city
wastes. Either can be mixed with gasoline, but ethanol is preferred.
The{{U}} {{U}} 5 {{/U}} {{/U}}fuel, methanol, can be{{U}}
{{U}} 6 {{/U}} {{/U}}by extra refining processes, but this increases
the cost and{{U}} {{U}} 7 {{/U}} {{/U}}the energy input-output
ratio. Service stations{{U}} {{U}} 8 {{/U}} {{/U}}the country
are already selling gasohol．{{U}} {{U}} 9 {{/U}}
{{/U}}discouragement from many large oil companies, ethanol may provide a
sensible, quick alternative to fossil fuels. Still{{U}}
{{U}} 10 {{/U}} {{/U}}alternative to fossil fuels can be{{U}}
{{U}} 11 {{/U}} {{/U}}in energy from the sun.{{U}} {{U}}
12 {{/U}} {{/U}}energy provides a good{{U}} {{U}} 13
{{/U}} {{/U}}of heat that can be collected and even{{U}} {{U}}
14 {{/U}} {{/U}}for later use. Already many homes and office buildings
have been designed to take{{U}} {{U}} 15 {{/U}} {{/U}}of the
sun's warmth. The sun can also be used to produce electricity.
Solar energy generators are already providing power for{{U}} {{U}}
16 {{/U}} {{/U}}Indian villages in Arizona and{{U}} {{U}}
17 {{/U}} {{/U}}in Alaska. Solar-generated electricity also may be the
airplane fuel of the future. Solar-powered aircraft have succeeded in crossing
the English Channel and{{U}} {{U}} 18 {{/U}} {{/U}}may
become{{U}} {{U}} 19 {{/U}} {{/U}}for extended distances, as
more efficient, lighter, and cheaper solar{{U}} {{U}} 20
{{/U}} {{/U}}are developed.