On Average, Errors Occur in DNA Synthesis Only Once in Every

On average, errors occur in DNA synthesis only once in every ten billion nucleotides incorporated. Which of the following does NOT contribute to this high fidelity of DNA synthesis?

A) Complementary base-pairing between the nucleotides
B) "Tightening" of the DNA polymerase enzyme around its active site to ensure correct pairing before monomer incorporation
C) Exonucleolytic proofreading by the 3′-to-5′ exonuclease activity of the enzyme to correct mispairing even after monomer incorporation
D) A strand-directed mismatch repair system that detects and resolves mismatches soon after DNA replication
E) All of the above mechanisms DO contribute to the fidelity.