Which Describes the Mechanism of Atorvastatin's (Lipitor) Ability to Lower

Which describes the mechanism of atorvastatin's (Lipitor) ability to lower blood cholesterol levels?

A) Binds exogenous cholesterol and excreting it in the feces
B) Increases excretion by activating enzymes within the hepatic system
C) Prevents dietary absorption within the GI tract
D) Inhibits an enzyme that is essential for cholesterol synthesis