**Core Concept**
The human plasma lipoproteins are a family of lipoproteins that transport lipids, including triacylglycerol (also known as triglycerides), cholesterol, and other lipophilic substances throughout the body. The composition and function of lipoproteins vary, and they are classified based on their density and protein content.

**Why the Correct Answer is Right**
Chylomicrons are the largest and least dense lipoproteins, primarily responsible for transporting dietary triacylglycerol from the small intestine to peripheral tissues and the liver. Their high triacylglycerol content is due to the fact that they are synthesized in the small intestine and contain a large amount of dietary fat from the ingested food. The apolipoprotein B-48 (apoB-48) is a key structural protein of chylomicrons, which helps to assemble and transport these lipoproteins.

**Why Each Wrong Option is Incorrect**
**Option A:** VLDL (Very Low-Density Lipoprotein) - While VLDL also contains a significant amount of triacylglycerol, it is primarily synthesized in the liver and has a higher protein content compared to chylomicrons. Thus, it is not the lipoprotein with the highest percentage of triacylglycerol by weight.

**Option B:** HDL (High-Density Lipoprotein) - HDL is known as "good cholesterol" and contains a high proportion of cholesterol relative to its phospholipid and protein content. However, it has a very low triacylglycerol content.

**Option D:** LDL (Low-Density Lipoprotein) - LDL is often referred to as "bad cholesterol" and is primarily involved in transporting cholesterol from the liver to peripheral tissues. While it does contain some triacylglycerol, its primary function and composition make it less relevant to triacylglycerol transport.

**Clinical Pearl / High-Yield Fact**
Chylomicrons are the primary lipoproteins responsible for transporting dietary fat, and their metabolism is impaired in conditions such as hypertriglyceridemia and lipoprotein lipase deficiency. Understanding the role of chylomicrons in lipid metabolism is essential for managing patients with dyslipidemia.

**Correct Answer: C. Chylomicrons**