The correct option is A Nirenberg & Matthaei
Marshall Nirenberg and Heinrich J. Matthaei were the first to elucidate the nature of a codon in 1961 at the National Institutes of Health. They used a cell-free system to translate a poly-uracil RNA sequence and discovered that the polypeptide that they had synthesized consisted of only the amino acid phenylalanine.They, thereby, deduced that the codon UUU specified the amino acid phenylalanine.