4. 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. (C-p8-16)
本句没有补出,是否说明也可以不补出,当然补出更好?
欢迎光临 国际顶尖MBA申请交流平台--TOPWAY MBA (http://forum.topway.org/) | Powered by Discuz! 7.2 |