Answer: A double-stranded DNA molecule is unwound into single strands. Polymerase matches the right nucleotides to the single strand so that each forms a double strand of DNA.
Explanation: During replication, a double-stranded DNA molecule is unwound by an enzyme known as helicase into two single strands of DNA that serve as templates for new strands of DNA.
Then another enzyme known as DNA polymerase matches the free and right nucleotides to the nucleotides on the single DNA strands (templates) to form a double-stranded DNA molecule.