Acetylcholinesterase (ache) is a protein that catalyzes the conversion of acetylcholine to acetate and choline. when the concentration of ache in an aqueous solution is held constant, the rate of the reaction catalyzed by ache increases with increasing concentrations of substrate. at low concentrations of acetylcholine, a small increase in the substrate concentration results in a large increase in the reaction rate. at high concentrations of acetylcholine, however, a large increase in the substrate concentration results in only a small increase in the reaction rate.
which of the following statements correctly explains the observed effect of the acetylcholine concentration on the rate of the enzyme-catalyzed reaction?

a. the active site of ache is specific for acetylcholine, and only one substrate molecule can occupy the active site at a time.
b. ache begins converting product into substrate as the acetylcholine concentration changes from low to high.
c. the ache protein becomes denatured as the acetylcholine concentration changes from low to high.
d. the substrate specificity of ache changes as the acetylcholine concentration changes from low to high.