Final answer:
If a tRNA with an anticodon of 5'-CAA-3' that is charged with methionine is added to a cell-free translation system, methionine would be incorporated into proteins at some positions where valine should be. The correct answer is c).
Step-by-step explanation:
If a tRNA with an anticodon of 5'-CAA-3' that is charged with methionine is added to a cell-free translation system, it would lead to methionine being incorporated into proteins at some positions where valine should be. This is because the tRNA, with its modified anticodon, would still recognize the codon that normally specifies valine, but instead deliver methionine due to its modified amino acid. Therefore, option C) methionine would be incorporated into proteins at some positions where valine should be is the correct prediction.