**Core Concept**
The question is inquiring about the primary form of DNA that is observed in cells. The correct answer pertains to the double-stranded, antiparallel structure of DNA, which is crucial for its replication, transcription, and repair processes.

**Why the Correct Answer is Right**
The double-stranded form of DNA is predominantly seen due to the complementary base pairing between the two strands, facilitated by hydrogen bonding between adenine (A) and thymine (T), and guanine (G) and cytosine (C). This antiparallel arrangement allows for the correct replication and transcription of genetic information. The double helix structure of DNA was first described by James Watson and Francis Crick in 1953.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a recognized form of DNA. While there are various forms of DNA, such as supercoiled, relaxed, or nicked, single-stranded DNA is not the primary form observed in cells.
* **Option B:** This option is incorrect because it does not accurately describe a recognized form of DNA. There is no widely accepted term "linear DNA" that refers to a specific form of DNA.
* **Option C:** This option is not correct because it does not describe the primary form of DNA. While circular DNA is observed in some organisms, such as bacteria, it is not the predominant form of DNA in eukaryotic cells.

**Clinical Pearl / High-Yield Fact**
DNA repair mechanisms, such as base excision repair (BER) and nucleotide excision repair (NER), are essential for maintaining the integrity of the double-stranded DNA structure. Deficiencies in these repair mechanisms can lead to genetic disorders and increased cancer susceptibility.

**Correct Answer:** C. Double-stranded DNA.