**Core Concept**
DNA (Deoxyribonucleic acid) is a double-stranded helix composed of nucleotides, which contain a sugar molecule called deoxyribose, a phosphate group, and one of four nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The unique base pairing between these nitrogenous bases is crucial for the stability and replication of DNA.

**Why the Correct Answer is Right**
The correct answer is that DNA has a double-stranded helix structure, which allows it to store genetic information in a compact and stable manner. The base pairing between adenine and thymine (A-T) and between cytosine and guanine (C-G) is specific and complementary, enabling the replication of DNA during cell division. This base pairing is facilitated by the hydrogen bonding between the nitrogenous bases, which helps to stabilize the double helix structure of DNA.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as DNA does not have a single-stranded structure. The double-stranded helix is essential for the stability and replication of DNA.
* **Option B:** This option is incorrect as DNA does not have a triple-stranded structure. The double-stranded helix is the characteristic structure of DNA.
* **Option C:** This option is incorrect as DNA does not have a triple-helix structure. The double-stranded helix is the characteristic structure of DNA.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the base pairing between adenine and thymine (A-T) and between cytosine and guanine (C-G) is specific and complementary, enabling the replication of DNA during cell division. This base pairing is crucial for the stability and accuracy of DNA replication.

**Correct Answer: C. Double-stranded helix structure.**