**Core Concept**
DNA replication is a crucial process in cell biology where DNA is copied to produce two identical daughter strands. Various mechanisms and enzymes are involved in this process. Some substances can interfere with DNA replication by incorporating into the DNA strand, thereby blocking it.

**Why the Correct Answer is Right**
The correct answer is a type of nucleoside analog, specifically a thymidine analog. When incorporated into the DNA strand, it causes chain termination during DNA replication. This is because it lacks the 3'-hydroxyl group necessary for phosphodiester bond formation. This results in the formation of a phosphodiester bond between the 5'-hydroxyl group of the nucleoside analog and the 3'-phosphate group of the adjacent nucleotide, effectively terminating the DNA strand. This process is known as chain termination.

**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because it is not a thymidine analog and does not cause chain termination during DNA replication.

**Option B:** This is incorrect because it is not a nucleoside analog and does not interfere with DNA replication by incorporating into the DNA strand.

**Option C:** This is incorrect because it is not a nucleoside analog and does not cause chain termination during DNA replication.

**Clinical Pearl / High-Yield Fact**
Nucleoside analogs, such as the correct answer, are used as antiviral agents to treat viral infections, such as HIV and herpes simplex virus. They work by inhibiting viral DNA replication, thereby reducing the viral load in the body.

**Correct Answer:** C. Azidothymidine (AZT) is a nucleoside analog that blocks DNA replication by getting incorporated in the DNA strand.