**Core Concept**
The cell membrane is a complex structure composed of lipids and proteins, with proteins making up a significant portion. The approximate composition of proteins in the cell membrane is crucial for understanding its function and integrity.

**Why the Correct Answer is Right**
The correct answer is approximately 50% protein, as the cell membrane is a dynamic structure where proteins are embedded or associated with the lipid bilayer, facilitating various cellular functions such as transport, signaling, and cell-cell interactions. This composition allows for the proper functioning of membrane-bound enzymes, receptors, and transport proteins.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it underestimates the protein composition.
**Option B:** This option overestimates the protein composition, which is not accurate for the cell membrane.
**Option D:** This option also underestimates the protein composition, neglecting the significant role proteins play in the cell membrane.

**Clinical Pearl / High-Yield Fact**
The protein composition of the cell membrane is crucial for understanding cellular functions and interactions, particularly in the context of disease mechanisms and drug targeting.

**Correct Answer:** C. 50% protein