The Department of Energy（DOE）is dealing with a tough research problem that has troubled experts for more than a decade： developing a low-cost alternative to the present jet fuel.
The search began around 2010，originally pushed by the concerns about the country's reliance on imported oil. More recently,airlines have raised the question themselves. There are potential restrictions on the amount of carbon dioxide from jet airliners and a lack of an electricity-fueled replacement for their heavy planes.
Researchers at DOE's National Renewable Energy Laboratory（NREL）are taking a fresh look at a promising family of new and plentiful raw materials：food wastes and urban used water containing human manure （粪肥）.
"Everyone is beginning to see the potential of taking these organic materials that we normally have sent to landfills or wastewater treatment plants," said Derek Vardon,a senior research engineer at NREL. Manure and food wastes contain fatty acids that can be changed to link their chain-like structures together. The result is a liquid fuel, Vardon explained, one that has seven times the energy of methane --- the major component of natural gas. That's needed to get a heavy airliner off the ground.
Other researchers are also sensing the potential of rich and low-carbon resources that could be developed by working with wastewater treatment plants. One of them is Jianping Yu,the main researcher of a separate NREL project that is exploring how to remove major and troublesome water pollutants from conventional wastewater treatment processes. His idea is to feed the pollutants to algae（海藻）in the wastewater plants and then sell the algae as a product that can be made into commercial fertilizers（肥料）. Yu's idea is to collect and develop special algae, so they can remove as much as 50% of the pollutants from processed wastewater. Growing more powerful algae, he points out, will also be a way to remove more CO₂ from the air. The outcome is that it could reduce the amount of energy needed to run wastewater plants. "That's the goal. Our main motivation is future environmental requirements," Yu said.



Why are the airlines anxious to find a new kind of jet fuel？ ______

A. Their planes are heavier than before.
B. They want to rely less on imported oil.
C. Their oil fuel harms the environment.
D. They need to cut costs of electrical energy.

What can we learn about the liquid fuel according to Vardon？ ______

A. It has as much energy as natural gas.
B. It's born out of organic wastes.
C. It can be changed into fatty acids.
D. It is similar to natural gas in structure.

What role do algae play in Jianping Yu's idea？ ______

A. Cleaning processed wastewater.
B. Producing green fuel.
C. Making commercial fertilizers.
D. Absorbing wastewater.

What does the text mainly tell us？ ______

A. Search for clean jet fuel leads scientists to wastewater plants.
B. Researchers find a way of environmental protection.
C. Wastewater plants are a very useful source of new energy.
D. Developing new fuel is quite necessary for airlines.