The correct option is A Nucleus
Messenger RNA (mRNA) is produced within the nucleus of a cell and migrates to the cytoplasm, where it attaches to ribosomes and guides the building of the amino acid sequences that will compose proteins. Ribosomes are sites for the meeting and binding of mRNA and transfer RNA (tRNA). They are the structures where amino acids transported by tRNA are united by peptide bonds to form polypeptide chains (proteins).