**Core Concept**
DNA (Deoxyribonucleic acid) is a double-stranded helix composed of nucleotides, each containing a phosphate group, a sugar molecule (deoxyribose), and one of four nitrogenous bases: adenine (A), guanine (G), cytosine (C), or thymine (T). The unique base pairing between adenine and thymine, and guanine and cytosine, forms the foundation of DNA structure.

**Why the Correct Answer is Right**
The correct answer highlights the significance of DNA's double-stranded structure and the base pairing rules. The sugar-phosphate backbone of DNA is outside the helix, while the nitrogenous bases project inward and pair with each other. Adenine always pairs with thymine through two hydrogen bonds, and guanine always pairs with cytosine through three hydrogen bonds. This base pairing is crucial for DNA replication and repair.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option might be incorrect if it contradicts the established base pairing rules or misrepresents the DNA structure.
* **Option B:** This option could be wrong if it fails to acknowledge the sugar-phosphate backbone or misattributes a specific property of DNA to a different molecule.
* **Option D:** This option might be incorrect if it introduces a concept not supported by current scientific understanding or misrepresents the double-stranded nature of DNA.

**Clinical Pearl / High-Yield Fact**
Remember the base pairing rules: A-T and G-C. This simple yet crucial concept underlies DNA replication, repair, and gene expression.

**Correct Answer: C. The base pairing rules are A-T and G-C.**