If two scientists at Los Alamos National Laboratory are correct，people will still be driving gasoline powered cars 50 years from now，giving out heat-trapping carbon dioxide（二氧化碳） into the atmosphere-and yet that carbon dioxide will not contribute to global warming.
    In a proposal by two scientists，vehicle emissions（排放） would no longer contribute to global warming.The scientists，F(xiàn).Jeffrey Martin and William L.Kubic Jr.，are proposing a concept，which they have named Green Freedom，for removing carbon dioxide from the air and turning it back into gasoline.
    The idea is simple.Air would be blown over a liquid solution of potassium carbonate，which would absorb the carbon dioxide.The carbon dioxide would then be put to chemical reactions that would turn it into fuel（燃料）：gasoline or jet fuel.
    This process could change carbon dioxide from an unwanted，climate-changing pollutant into a vast resource for renewable fuels.The cycle-equal amounts of carbon dioxide produced and removed-would mean that cars，trucks and airplanes using the synthetic（合成的） fuels would no longer be contributing to global warming.
    Although they have not yet built a synthetic fuel factory，or even a small model，the scientists say it is all based on existing technology."Everything in the concept has been built，is operating or has a close cousin that is operating."Dr.Martin said.
    The Los Alamos proposal does not go against any laws of physics，and other scientists who have independently suggested similar ideas.Dr.Martin said he and Dr.Kubic had worked out their concept in more detail than former proposals.
    There is，however，a major fact that explains why no one has built a carbon-dioxide-to-gasoline factory：it requires a great deal of energy.
    According to their analysis，their concept，which would cost about＄5 billion to build，could produce gasoline at an operating cost of＄1.40 a gallon and would turn economically practical when the price at the pump hits＄4.60 a gallon.
    Other scientists said the Los Alamos proposal perhaps looked promising but could not evaluate it fully because the details had not been published."It's definitely worth pursuing，"said Martin I.Hoffert，a professor of physics at New York University."It's not that new an idea.It has a couple of pieces to it that are interesting."

（1）What is the value of the scientists' proposal？

C

C

A．It increases the productivity of a fuel factory
B．It decreases the cost of producing gasoline
C．It reduces the pollution caused by car driving
D．It promotes a new idea of environmental protection
（2）The underlined part"has a close cousin that is operating"probably means the technology in the concept

D

D

.
A．has been popular for so long
B．has been ignored by many people
C．is not appropriate for practice
D．will be put into practice in the near future
（3）What is the biggest challenge in realizing the concept Green Freedom？

B

B

A．There is no theoretical basis.
B．It is not economically practical.
C．There is no solution to some technical problems.
D．Only a few scientists support the idea.