**Core Concept**
Myelin is a complex lipid-protein structure that surrounds and insulates the axons of neurons, facilitating efficient transmission of nerve impulses. The myelin sheath is composed of a lipid-rich compacted layer of glial cell membranes, with interspersed proteins that contribute to its structural integrity and function.

**Why the Correct Answer is Right**
The protein-to-lipid ratio in myelin is approximately 1:5, indicating that lipids constitute the majority of its composition. This high lipid content allows for efficient electrical insulation and facilitates the rapid propagation of action potentials along the axon. The lipids in myelin, particularly galactocerebroside and sulfatide, contribute to its compact structure and hydrophobic properties.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because myelin does not have a protein-to-lipid ratio of 5:1, which would suggest an extremely high protein content.
**Option B:** This option is incorrect because myelin's protein-to-lipid ratio is not 20:1, which would imply a much higher protein content than is actually the case.
**Option C:** This option is incorrect because myelin's protein-to-lipid ratio is not 1:20, which would suggest a much lower protein content than is actually the case.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the myelin sheath is composed of a lipid-rich compacted layer of glial cell membranes, with interspersed proteins that contribute to its structural integrity and function. This lipid-rich composition allows for efficient electrical insulation and facilitates the rapid propagation of action potentials along the axon.

**Correct Answer: C. 1:20.**