What allows DNA polymerase III to add the first DNA nucleotides during replication?

DNA polymerase III requires a primer with a free -OH (hydroxyl) group to initiate the addition of nucleotides during DNA replication. This is because DNA polymerases can only extend an existing strand, meaning they cannot start de novo synthesis without a primer. In this context, the RNA primer serves as the starting point for replication.

An RNA primer, synthesized by primase, provides the necessary -OH group at its 3' end, allowing DNA polymerase III to begin adding DNA nucleotides complementary to the template strand. This primer is crucial because it stabilizes the starting point for DNA synthesis, aligning with the template DNA strand, thereby facilitating the replication process.

Other options lack the critical feature of providing a suitable -OH end for nucleotide addition. For instance, while a DNA primer can also provide an -OH end, it is not the correct answer in this case since the initial nucleotides added during replication are indeed synthesized using an RNA primer. Thus, recognizing the role of the RNA primer in enabling DNA polymerase III to initiate synthesis highlights why this choice is correct.