TRNA have the ability  to match a codon to the appropriate antoicodon by using its own complementary anticodon. its just like a key and a lock that a  key fits you know, when you got your right key.
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T-rna has the anticodon which is the perfect complementary match of a codon so if a codon has GAC then the anticodon will have CUG. it just like matching complementary bases  in the copying of DNA
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