The right answer is DNA synthesis.
In chemistry, a dehydration reaction is a chemical reaction in which the starting reagent loses a hydrogen atom and a hydroxyl group, a molecule of water, the reverse of the hydration reaction. Dehydration reactions are a subset of the elimination reactions.
In the case of DNA synthesis:
d (NTP) n + dNTP -> d (NMP) n + 1 + PPI + H2O