Answer the following question given this paragraph: 

The genetic code works as a series of three-letter codes. Each sequence of three letters, called a triplet, corresponds to one of the twenty common amino acids. The triplets are read by the cell, one after the other, in the process of protein synthesis. The Table below shows all of the possible triplets and the amino acids that result from each three-letter code.


Q: In what kind of a series does the genetic code work?


A:
three-letter codes