The genetic code contains 61 codons to specify the 20 common amino acids. Many organisms carry fewer than 61 different tRNA genes in their genomes. These genomes take advantage of isoaccepting tRNAs and the rules governing third-base wobble to encode fewer than 61 tRNA genes.

Use these rules to calculate the minimal number of tRNA genes required to specify all 20 of the common amino acids.

a.20
b. 26
c. 27
d. 31
e. 35
f. 42