Answer:
Because of the codon oscillation.
Step-by-step explanation:
The formation of codons is susceptible to the occurrence of oscillation, which is the term that corresponds to the fact that many codons have synonyms in the third position, that is, in the third letter. For example, the codon CUA, which represents leucine, will also represent leucine if it is presented in CUU, CUC and CUG forms, due to the oscillation in the third position. This allows the tRNA to recognize any of these codons and pair with the anticodon smoothly and without errors.