Yet cleaning gasoline and diesel fuel emissions is very dif ficult problem. More and more cars and motorcycles use environmental protection as a selling point. But given how they work--burning fuel to produce power-- and the laws of physics, their engines are bound to emit something.
愈來愈多的汽機車以環保做賣點，但汽車的本質﹘ ﹘燃燒汽油產生動力，在物質不滅定律下，總得釋出點什麼東西。