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.