Explanation
In eukaryotes, mRNA is synthesized with the aid of RNA Polymerase II. Therefore, the answer is B) RNA Polymerase II.
RNA Polymerase II is responsible for transcribing protein-coding genes into mRNA, which is then processed and transported out of the nucleus for translation into proteins. RNA Polymerase III is responsible for transcribing genes that produce small RNA molecules such as tRNA and some small nuclear RNA (snRNA), while RNA Polymerase I transcribes genes that produce the precursors of ribosomal RNA (rRNA). Reverse transcriptase is an enzyme found in retroviruses that converts RNA into DNA.
