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 around its active site to ensure correct pairing before monomer incorporation (C) 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) None of the above