**Core Concept**
The polymerase chain reaction (PCR) is a laboratory technique used to amplify specific DNA sequences. This process involves the action of enzymes that facilitate the synthesis of new DNA strands from a template DNA.

**Why the Correct Answer is Right**
The correct answer is Taq polymerase. Taq polymerase is a heat-stable DNA polymerase enzyme extracted from the bacterium *Thermus aquaticus*. It plays a crucial role in PCR by synthesizing new DNA strands from the template DNA. Taq polymerase has a high temperature tolerance, allowing it to function optimally at the high temperatures required for the denaturation step of PCR. Additionally, Taq polymerase has a 5' to 3' exonuclease activity, which helps in proofreading and correcting errors during DNA synthesis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Reverse transcriptase is an enzyme used for converting RNA into DNA, not for DNA amplification in PCR.
* **Option B:** DNA ligase is an enzyme that seals gaps between DNA fragments, but it is not involved in the PCR process.
* **Option C:** Helicase is an enzyme that unwinds double-stranded DNA into single strands, but it is not directly involved in DNA synthesis during PCR.

**Clinical Pearl / High-Yield Fact**
Taq polymerase is heat-stable due to its unique structure, which includes a high content of thermostable proteins. This property allows Taq polymerase to function optimally at high temperatures, making it an essential enzyme in PCR.

**Correct Answer:** C. Taq polymerase.