What is a triplet codon?

The correct option is B Degenerate
The genetic code consists of 64 triplets of nulceotides. These triplets are called codons. With three exceptions, each codon encodes for one of the 20 amino acids used in the synthesis of proteins. That produces some redundancy in the code: most of the amino acids being encoded by more than one codon, which is called as degeneracy of the genetic code.