有一道语法题的答案是:Because natural gas is composed mostly of methane, a simple hydrocarbon, vehicles powered by natural gas emit less of certain pollutants than those burning gasoline or diesel fuel.请问为什么要在比较结构中省略助动词do.白勇说比较结构中be动词可省可不省,但是助动词不能省,为什么答案不是than those burning gasoline or diesel fuel do 呢
以下是引用turtlechen在2004-1-5 1:18:00的发言: 我覺得這句話已經做過省略了。我猜原來是這樣的: vehicles powered by natural gas emit less of certain pollutants than vehicles burn (=those burning ) gasoline or diesel fuel.