The correct option is D Holley, Nirenberg and Khorana
Marshall Nirenberg identified the first triplet codon, which was UUU for phenylalanine. Har Gobind Khorana extended Nirenberg's work, and eventually, by 1965, Nirenberg and Khorana with their colleagues had deciphered the entire genetic code. For their contributions, Nirenberg and Khorana, along with another genetic code researcher, Robert Holley, received the Nobel Prize in 1968.