单项选择题
Henry and Tom（）to the particles at the Trade Union every Saturday.
A.used to go B.were used to go C.are used to go D.ues to go
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.
单项选择题 All of these alternatives are carbon-based fuels（）molecules are smaller and simpler than those of gasoline.
