????4.酒精和彈性燃料

????2007年，美國政府出臺了《再生燃料法案》（Renewable Fuels），要求汽油中必須添加一定量的用再生能源制成的液體，這讓用玉米加工的酒精得以進入美國的燃料供應(yīng)體系。共有84種汽車或卡車使用了指定的“彈性燃料”，意味著它們的燃料最多可以包含85%的酒精。最近，針對酒精使用的批評正在抬頭，因為大家逐漸認識到，酒精所含的能量比汽油少，導(dǎo)致每加侖燃油行駛的里程數(shù)減少，同時酒精生產(chǎn)卻需要消耗大量的能量，而這又會導(dǎo)致二氧化碳排放增加。反對者還聲稱，使用酒精也是不道德的，因為它占用了食物供應(yīng)中40%的玉米，同時推高了玉米的價格。

????4. Ethanol and flex fuel

????Thanks to the government's 2007 Renewable Fuels mandate requiring a certain amount of liquids made from renewable sources to be added to gasoline, ethanol made from corn has found its way into the nation's fuel supply. Some 84 car and truck models carry the designation "flex fuel," meaning they can run on mixtures that contain up to 85% ethanol. Lately, a backlash against ethanol use has developed as realization grows that ethanol contains less energy than gasoline, resulting in fewer miles per gallon, and takes a lot of energy to produce, which can lead to increased emissions of carbon dioxide. Opponents also argue that ethanol is unethical, because it diverts 40% of the corn grown from food supplies and drives up its cost.