单项选择题
Although recent years have seen substantial reductions in noxious pollutants from individual motor vehicles, the number of such vehicles（）.
A.have been steadily increasing B.has been steadily increased C.has been steadily increasing D.have been steadily increased
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.
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.
