Answer:
d. the 5' end
Explanation:
Capping is a co-transcriptional modification made to RNA in the nucleus after the first 25–30 nts are incorporated into the nascent transcript, which is synthetized in the 5' ---> 3' direction.
The cap consists of a methylated guanosine nucleotide added to the 5' end of the new mRNA transcript, and is important for several processes, which include: