**Core Concept**
The question targets the identification of a major lipid component of the mitochondrial membrane, which is a crucial aspect of cellular biology and biochemistry. Mitochondrial membranes are composed of various lipids, including phospholipids, cholesterol, and cardiolipin.

**Why the Correct Answer is Right**
Cardiolipin is a crucial lipid component of the mitochondrial inner membrane, playing a key role in maintaining the structural integrity and function of mitochondria. It is particularly abundant in the inner mitochondrial membrane, where it helps to stabilize the arrangement of proteins and facilitate the process of oxidative phosphorylation. The unique structure of cardiolipin, with its four acyl chains, allows it to interact with various proteins and other lipids, contributing to the overall organization and function of the mitochondrial membrane.

**Why Each Wrong Option is Incorrect**
**Option A:** While phospholipids are indeed a major component of cell membranes, they are not specifically characteristic of mitochondrial membranes. Phospholipids are a broad class of lipids that play a key role in maintaining membrane structure and function in various cellular contexts.
**Option B:** Cholesterol is an essential lipid component of many cell membranes, but it is not a major lipid of the mitochondrial membrane. Cholesterol is primarily found in the plasma membrane and plays a key role in regulating membrane fluidity and function.
**Option C:** Other lipids, such as phosphatidylethanolamine and phosphatidylserine, are also present in mitochondrial membranes but are not the major lipid component.

**Clinical Pearl / High-Yield Fact**
Cardiolipin is a key player in the regulation of mitochondrial dynamics and function, and alterations in its structure or function have been implicated in various diseases, including neurodegenerative disorders and metabolic disorders.

**Correct Answer: C. Cardiolipin**