Step 1: The question.
In PCR, which step uses DNA polymerase along with deoxynucleotides.
Step 2: The three PCR steps.
Each PCR cycle has denaturation, annealing, and extension.
Step 3: Denaturation and annealing.
Denaturation just heats the DNA to split the two strands. Annealing lets the short primers stick to the single strands. Neither of these needs the polymerase or the nucleotides yet.
Step 4: The extension step.
In extension, DNA polymerase, usually Taq polymerase, sits on the primer and adds deoxynucleotides, the dNTPs, one by one to build the new strand. So this step uses both.
Step 5: About amplification.
Amplification is the overall result of many cycles, not a single step, so it is not the answer.
Step 6: Conclusion.
Therefore the correct answer is "Extension". \[ \boxed{\text{Extension}} \]