**Core Concept**
Statins are a group of cholesterol-lowering medications that exert their effects through the inhibition of a key enzyme involved in cholesterol biosynthesis. This enzyme, HMG-CoA reductase, plays a central role in the conversion of HMG-CoA to mevalonate, a crucial step in the production of cholesterol in the liver.

**Why the Correct Answer is Right**
Statins, such as atorvastatin and simvastatin, specifically target HMG-CoA reductase, inhibiting its activity and thereby reducing the liver's ability to produce cholesterol. This decrease in cholesterol production leads to an increase in the expression of LDL receptors on the surface of liver cells, enhancing the clearance of LDL cholesterol from the bloodstream. The inhibition of HMG-CoA reductase also has a downstream effect on the production of isoprenoids, which are involved in the post-translational modification of small GTPases, such as Rho and Ras.

**Why Each Wrong Option is Incorrect**
**Option A:** HMG-CoA synthase is an enzyme involved in the biosynthesis of cholesterol, but it is not the primary target of statins. In fact, statins do not inhibit HMG-CoA synthase.
**Option B:** Stimulating HMG-CoA reductase would increase cholesterol production in the liver, which is the opposite of the desired effect of statins.
**Option D:** Stimulating HMG-CoA synthase would also increase cholesterol production, making it an incorrect choice.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that statins not only lower LDL cholesterol but also have pleiotropic effects, including anti-inflammatory properties, improvement of endothelial function, and reduction of platelet aggregation.

**✓ Correct Answer: C. Inhibit HMG CoA reductase**