The best explanation for what is occurring at the arrow (translation) is:
C. The codon on the mRNA pairs with the anticodon on the tRNA which transfers amino acids into the proper sequence to form a protein.
In translation, the sequence of codons on the mRNA is read by tRNA molecules, which have complementary anticodons. This process allows the tRNA to bring the appropriate amino acids to the growing polypeptide chain, forming a protein molecule.