The correct option is
B removal of introns from pre mRNA to produce the final set of instructions for the protein
The gene encoding for mRNA has two types of sequences called the introns and the exons. The introns are the intervening sequences and they do not code for a functional polypeptide. The exons are the functional sequences. However, the exons are intervened by the introns. When such a gene is transcribed, the RNA so formed will have both these sequences. Such an RNA is called the hnRNA (heterogeneous RNA) or the pre-mRNA. This pre-mRNA undergoes a post-transcriptional modification called the splicing where these introns are removed from the pre-mRNA. The RNA obtained after the process of splicing is called the mRNA and it has the sequences for only exons, that will be translated to form a functional polypeptide.
Hence, the correct answer is 'removal of introns from pre mRNA to produce the final set of instructions for the protein'.