此外乙醇的制造得耗用大量石化燃料，两相抵扣之后、我们最后得到的干净能源量其实并没那么高。
Furthermore, ethanol requires a tremendous amount of fossil fuels to produce. The net energy gain is not terribly high.
它们运行依靠优良古老的干净人类能源——多余的卡路里和一点体力活。
They run on good old clean human energy - extra calories and a bit of elbow grease.
能源意蕴被转化为字母等级，从非常干净的A级到脏污的G级。
The energy implications are converted into letter grades, from squeaky-clean A to dirty G.
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