Final answer:
The step following the unzipping of DNA during replication is the pairing of complementary nitrogen bases with the DNA strands to form new DNA molecules.
Step-by-step explanation:
After DNA is unzipped, the next step in DNA replication is C. Nitrogen bases pair up with the DNA strands. During this phase, enzymes called DNA polymerases add complementary nucleotides to each of the original DNA strands, which serves as templates. These nucleotides are paired based on the base pairing rules with adenine (A) pairing with thymine (T) and cytosine (C) pairing with guanine (G) to form two identical DNA molecules, each consisting of one original strand and one newly synthesized strand.