Final answer:
The tRNA matches its anticodon with the codon on mRNA to deliver the correct amino acid to the ribosome during protein synthesis, making option B the correct choice.
Step-by-step explanation:
Transfer RNA (tRNA) is responsible for delivering the correct amino acids to the ribosome during protein synthesis. It does so by matching its anticodon with the codon on mRNA. So, the answer to the student's question is, tRNA "knows" which amino acid it needs to drop off at the ribosomes by matching its anticodon with the codon on mRNA, hence option B is the correct answer.
Even if a tRNA is chemically modified to carry a different amino acid than the one specified by its anticodon, the tRNA recognizes the codon in the mRNA specified by its anticodon, not the chemically modified amino acid it carries. Thus, a tRNA with an AAG anticodon would link to the AAG codon in the mRNA, ensuring that the correct amino acid (as determined by the anticodon, not the modification) is added to the growing polypeptide chain.