**Core Concept**
The unwinding of DNA is a crucial step in DNA replication, allowing the replication machinery to access the genetic material. This process involves the unwinding of the double helix structure of DNA, creating a replication fork where the DNA is separated into two strands.

**Why the Correct Answer is Right**
The correct answer is an enzyme that plays a key role in the unwinding of DNA by cutting the phosphodiester backbone of DNA. This enzyme is essential for the initiation of DNA replication, as it creates the replication fork and allows the replication machinery to access the genetic material. The enzyme works by hydrolyzing the phosphodiester bonds between the nucleotides, creating a single-stranded DNA template that can be used for replication.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because while it is involved in DNA repair, it is not responsible for the unwinding of DNA during replication.
**Option B:** This option is incorrect because it is involved in the degradation of DNA, not the unwinding of DNA during replication.
**Option C:** This option is incorrect because it is involved in the modification of DNA, not the unwinding of DNA during replication.

**Clinical Pearl / High-Yield Fact**
The unwinding of DNA during replication is a highly regulated process that is essential for the accuracy and fidelity of DNA replication. The enzyme responsible for this process is a crucial target for cancer therapy, as its inhibition can prevent the replication of cancer cells.

**Correct Answer:** B. Helicase.