Motor-cycles come in both two-cycle and four-cycle models, and two-cycle engines use a mixture of gasoline and diesel fuel, which produces a great deal of carbon monoxide and other pollutants.
汽機車由於引擎構造的關係，有二、四行程之別。所謂二行程，就是引擎在進氣、壓縮、推進、掃氣（排氣）等四道手續中，少了兩個動作，如此使不少汽油根本未經燃燒就排放出去、造成汙染。「二行程」淘汰不了？