单项选择题
Vehicles（）only the simplest of the engine improvements that methanol makes feasible would still contribute to an immediate lessening of urban air pollution.
A.corporate B.cooperating C.operating D.incorporating
单项选择题 Henry and Tom（）to the particles at the Trade Union every Saturday.
单项选择题 Ethanol is commonly used（）a gasoline supplement.
单项选择题 The combustion of larger molecules,（）have multiple carbon-carbon bonds involves a more complex series of reactions.
