The correct answer is option 3, which states that Marshall Nirenberg, Severo Ochoa, and Hargobind Khurana contributed to deciphering the genetic code.

Option 1, J.D. Watson and Francis Crick were not directly involved in deciphering the genetic code. They are renowned for their discovery of the structure of DNA, but deciphering the genetic code involved a different set of experiments and researchers.

Option 2, Linus Pauling, while a prominent figure in the field of chemistry, did not specifically contribute to deciphering the genetic code. His work focused more on protein structure.

Option 4, Barbara McClintock, was a pioneering researcher, but her contributions were mainly in the field of genetics and the discovery of "jumping genes" called transposons. Her work did not directly involve deciphering the genetic code.

Therefore, the correct answer is option 3, as Marshall Nirenberg, Severo Ochoa, and Hargobind Khurana made significant contributions to understanding the genetic code. They conducted groundbreaking experiments that led to the identification of codons and the correspondence between specific sequences of DNA and amino acids.