Why does the incorporation of a dideoxynucleotide into a growing DNA strand result in chain termination?

• A. They contain a reactive sulfur group that cleaves the DNA
• B. Dideoxynucleotides have an extra phosphate group that blocks elongation
• C. They form unstable bonds with adjacent nucleotides
• D. Dideoxynucleotides lack a 3' hydroxyl group, preventing further extension

Answer: (D)