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