**Core Concept**
Apo-E and apo C-II are important apolipoproteins involved in lipid metabolism. Apo-E plays a crucial role in the clearance of triglyceride-rich lipoproteins, including chylomicrons, from the bloodstream. Apo C-II is a cofactor for lipoprotein lipase, which is essential for the breakdown of triglycerides in chylomicrons.

**Why the Correct Answer is Right**
HDL (High-Density Lipoprotein) is the primary source of apo-E and apo C-II for chylomicrons. HDL particles are unique in that they can accept and transfer apolipoproteins to other lipoproteins. Apo-E and apo C-II are transferred from HDL to chylomicrons, allowing them to be efficiently cleared from the bloodstream by the liver. This process is facilitated by the presence of apo-E, which binds to specific receptors on the surface of liver cells, leading to the uptake and degradation of chylomicrons.

**Why Each Wrong Option is Incorrect**
**Option A:** VLDL (Very-Low-Density Lipoprotein) is a triglyceride-rich lipoprotein that is produced in the liver and is not a source of apo-E and apo C-II for chylomicrons.
**Option B:** IDL (Intermediate-Density Lipoprotein) is a remnant of VLDL that has undergone partial clearance and is not a source of apo-E and apo C-II for chylomicrons.
**Option C:** LDL (Low-Density Lipoprotein) is primarily involved in the transport of cholesterol to peripheral tissues and is not a source of apo-E and apo C-II for chylomicrons.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that HDL plays a critical role in the transfer of apolipoproteins to other lipoproteins, highlighting its importance in lipid metabolism and atherosclerosis prevention. HDL's role in apo-E and apo C-II transfer is a key aspect of its anti-atherogenic properties.

**✓ Correct Answer: D. HDL. HDL is the primary source of apo-E and apo C-II for chylomicrons.**