Answer:
d. RNA polymerase II.
Explanation:
The main enzyme responsible for RNA synthesis is RNA polymerase, which catalyzes the polymerization of 5'-triphosphate ribonucleosides (NTP) directed by a DNA mold.
Eukaryotic cells contain three types of nuclear RNA polymerases that transcribe different types of genes. Protein-encoding genes are transcribed by RNA polymerase II to give mRNA.