what did gould's theory of punctuated equilibrium state about the pace and timing of evolutionary change?
a. evolutionary change occurred gradually and constantly throughout time.
b. the pace of evolutionary change has slowed down over time and rarely occurs now.
c. periods during which evolution occurred were always preceded by a catastrophe.
d. long periods of stability were marked with periods of evolutionary change.

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.