Final answer:
Codons differing in the first two nucleotides require two different tRNA molecules to be recognized, as the first two nucleotides of a codon are critical for amino acid specification.
Step-by-step explanation:
Codons that differ in either of the first two nucleotides must be recognized by different tRNA molecules. The transfer RNA (tRNA) has the crucial role of matching amino acids to the appropriate codons in the mRNA during protein synthesis. Since the first two nucleotides of a codon play a critical role in specifying which amino acid is to be added to the polypeptide chain, a change in either of these nucleotides would typically require different tRNAs to recognize them. However, due to the presence of the wobble position at the third nucleotide, a single tRNA might recognize codons with different third nucleotides. Therefore, the answer is B. Two different tRNA molecules.