Which step happens first in DNA replication?

• A. Helicase unwinds the DNA double helix at the origin of replication, separating the strands
• B. Primase removes RNA primers and replaces them with DNA nucleotides
• C. DNA polymerase III adds nucleotides to elongate the new strand in the $5\prime$ to $3\prime$ direction
• D. DNA ligase seals nicks between Okazaki fragments on the lagging strand

Answer: (A)