**Core Concept**
Telomeres are repetitive nucleotide sequences located at the ends of chromosomes, crucial for maintaining chromosomal stability and preventing fusion with neighboring chromosomes. Telomerase is an enzyme responsible for lengthening telomeres, which is essential for the continuous division of cells.

**Why the Correct Answer is Right**
Telomerase is a reverse transcriptase enzyme that extends telomeres by adding nucleotides to the 3' end. This process counteracts the natural shortening of telomeres that occurs with each cell division due to the end-replication problem. Cancer cells, which exhibit immortality, express high levels of telomerase, allowing them to bypass the normal telomere shortening process and continue dividing indefinitely.

**Why Each Wrong Option is Incorrect**
**Option A:** DNA reverse transcriptase is an enzyme that synthesizes DNA from an RNA template, but it is not primarily responsible for telomere lengthening. Reverse transcriptase is a key enzyme in the life cycle of retroviruses, such as HIV.
**Option B:** RNA polymerase is an enzyme involved in transcription, the process of synthesizing RNA from a DNA template. While essential for gene expression, RNA polymerase is not directly involved in telomere maintenance.
**Option D:** DNA polymerase is an enzyme responsible for DNA replication and repair, but it is not specifically involved in telomere lengthening.

**Clinical Pearl / High-Yield Fact**
Telomerase activity is a hallmark of cancer cells and is often used as a biomarker for cancer diagnosis and prognosis. Inhibitors of telomerase are being explored as potential cancer therapeutics.

**✓ Correct Answer: C. Telomerase. Telomerase is the enzymatic mutation responsible for the immortality of cancer cells.**