**Core Concept**
The question is testing the student's understanding of the composition of lipoproteins, which are complex particles that transport lipids in the bloodstream. Lipoproteins consist of a lipid core surrounded by a protein shell, and their composition varies depending on their function and density.

**Why the Correct Answer is Right**
The major lipid of lipoproteins is cholesterol. Cholesterol is a sterol that plays a crucial role in various cellular processes, including membrane structure and signaling. It is transported in the bloodstream by lipoproteins, which help to distribute it to tissues throughout the body. The main lipoproteins involved in cholesterol transport are low-density lipoproteins (LDL) and high-density lipoproteins (HDL).

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided, as the question only has four options.
* **Option B:** This option is not relevant to the composition of lipoproteins. Lipoproteins do not primarily consist of triglycerides, although they can contain small amounts of triglycerides.
* **Option C:** This option is not correct. While lipoproteins do contain phospholipids, they are not the major lipid component. Phospholipids are present in the lipid bilayer of cell membranes and in the surface layer of lipoproteins, but cholesterol is the primary lipid.
* **Option D:** This option is not provided, as the question only has four options.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that high levels of LDL cholesterol are associated with increased risk of atherosclerotic cardiovascular disease, while high levels of HDL cholesterol are associated with reduced risk. Maintaining a healthy balance of cholesterol levels through diet, exercise, and medication can help prevent cardiovascular disease.

**Correct Answer:** C. Cholesterol.