(14 points) what nationwide step that greatly reduced dangerous automobile emissions was mandated by the u. s. clean air act?

a switch from gasoline-powered cars to hybrid gasoline-electric cars

a raising of the heights of factory chimneys that polluted

the gradual elimination of leaded gasoline as an auto fuel

a change from american cars to cars from other auto-producing nations

Lactase is essential for digesting lactose in milk. this enzyme is specific for this sugar. why? molecules and active sites vary in size; only properly sized molecules can fit.there is a precise compatibility between the active site and the lactose molecule.specificity refers to the action of the enzyme, such as hydrolysis, and relatively few molecules can be hydrolyzed.reaction-specific enzymes assume a fit by folding around the most numerous substrate molecules.