Transfer ribonucleic acid or tRNA is a type of RNA molecule that serves as an adaptor in translating the language of nucleic acids into the language of proteins. They are relatively small and consist of a single strand of RNA folded into a precise three-dimensional structure (the cloverleaf secondary structure). Most tRNAs have a guanylate (pG) residue at the 5' end and all have the trinucleotide sequence CCA (3') at the 3' end. The CCA tail of the amino acid arm is a cytosine-cytosine-adenine sequence at the 3' end of the tRNA molecule. The amino acid loaded onto the tRNA by aminoacyl tRNA synthetases, to form aminoacyl-tRNA, is covalently bonded to the 3'-hydroxyl group on the CCA tail. This sequence is important for the recognition of tRNA by enzymes and critical in translation. Therefore, option A is correct answer.