The correct answer is A) DNA polymerase.
DNA replication is a vital process in the cell cycle where the DNA makes a copy of itself. This process is facilitated by several key enzymes, each playing a specific role. DNA polymerase is the enzyme responsible for synthesizing new DNA strands. It does this by adding nucleotides to the 3′ end of an existing DNA strand, effectively elongating the new strand.
In contrast, helicase unwinds the double helix structure of the DNA, creating two single strands that serve as templates. Primase, on the other hand, synthesizes a short RNA primer that provides a starting point for DNA polymerase. Lastly, topoisomerase relieves the tension in the DNA strands caused by unwinding. Therefore, while all these enzymes are crucial for DNA replication, it is DNA polymerase that specifically adds nucleotides to the growing strand.