单项选择题 These reactions increase the probability of incomplete combustion and are more likely to（）uncombusted and photochemically active hydrocarbon compounds into the atmosphere.

单项选择题 There is a growing realization that the only effective way to achieve further reductions in vehicle（）is to replace conventional diesel fuel and gasoline with cleaner-burning fuels.

单项选择题 Consequently, more than 100 cities in the United States still have levels of carbon monoxide, particulate matter, and ozone that（）legally established limits.