During DNA replication, why is an RNA primer required?

• A. Primers are required to prevent DNA ligase from sealing Okazaki fragments before replication is complete.
• B. Primers are required because helicase cannot unwind the DNA duplex unless an RNA segment is first synthesized.
• C. DNA polymerases cannot initiate DNA synthesis de novo and require a free $3\prime OH$ group to add nucleotides.
• D. DNA polymerases can only add nucleotides in the $3\prime \to 5\prime$ direction, so a primer reverses the direction of synthesis.

Answer: (C)