Which desribes the main purpose of rna polymerase during transcription

The transcription of mRNA begins in the nucleus. The DNA is uncoiled and the nucleic acids with nitrogen bases adenine, thymine, guanine, and cytosine combine to form an incomplete mRNA. The current RNA contains exons (the coding region) and introns (non-informational regions). The introns are cut out and remaining exons are spliced together. Now the mRNA goes through polyadenylation. This is the process where the 3' end of the mRNA is attached with multiple adenine nucleotides. On the 5' end of the mRNA, a 5' cap is attached. This is the complete and functional mRNA. At this point, the mRNA exits the nucleus to join with the ribosome, ending the transcription and starting the process of translation.

Ithink it’s c or b for the answer.