The genetic code is how we call the combinations of three nucleotides (codons) that cells use to translate the information in the DNA and RNA in proteins.
There are 22 amino acids used to make proteins, but 64 possible codons, so some amino acids correspond to more than one codon. All proteins start with methionine (Met) and there are also codons that mark the end of a protein.
The codon for Met is AUG; and the stop codons are UAA, UAG, and UGA.
This means D is the right answer.