**Core Concept**
The process of synthesizing complementary DNA (cDNA) from RNA involves the conversion of a single-stranded RNA template into a double-stranded DNA molecule. This process is essential in molecular biology, allowing researchers to amplify specific DNA sequences and study gene expression. The key enzyme responsible for this conversion is reverse transcriptase.

**Why the Correct Answer is Right**
Reverse transcriptase is an enzyme that catalyzes the synthesis of cDNA from an RNA template. This process occurs in two stages: initiation and elongation. During initiation, the enzyme binds to the RNA template and forms a complex with a primer, which is a short DNA sequence complementary to the RNA. The primer is then extended by the addition of nucleotides, resulting in the formation of a complementary DNA strand. The enzyme continues to elongate the DNA strand by adding nucleotides to the 3' end, ultimately forming a double-stranded DNA molecule.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the enzyme responsible for cDNA synthesis. While DNA polymerase is involved in DNA replication, it is not the primary enzyme responsible for cDNA synthesis.
**Option B:** This option is incorrect because it is a type of DNA polymerase involved in DNA repair and replication, but not cDNA synthesis.
**Option C:** This option is incorrect because it is a type of RNA polymerase involved in transcription, not cDNA synthesis.

**Clinical Pearl / High-Yield Fact**
Reverse transcriptase inhibitors are a class of antiretroviral medications used to treat HIV infection. These medications work by inhibiting the activity of reverse transcriptase, thereby preventing the formation of cDNA from the viral RNA template.

**Correct Answer: D. Reverse Transcriptase. Reverse Transcriptase is the enzyme responsible for synthesizing cDNA from an RNA template.