Given below are two statements. One is labelled Assertion (A) and the other is labelled Reason (R).
Assertion (A): For long DNA molecules, the two strands of DNA cannot be separated at entire length, the replication occurs within a small opening of the DNA helix, referred to as a replication fork.
Reason (R): DNA strand unwinding and DNA polymerization require energy.
In light of the above statements, choose the correct answer from the options given below.

Assertion (A): For long DNA molecules, the entire length of both DNA strands cannot be simultaneously unwound and replicated. Instead, the DNA helix is opened up locally at the replication fork. This is because unwinding and replicating a long DNA molecule all at once would be energetically costly and impractical.
Reason (R): DNA strand unwinding and DNA polymerization do require energy. DNA helicase enzymes are responsible for unwinding the DNA strands, and ATP (adenosine triphosphate) provides the necessary energy for this process. DNA polymerases, which synthesize new DNA strands, also require energy in the form of nucleotide triphosphates (dATP, dCTP, dGTP, and dTTP) to add nucleotides to the growing DNA chain.
In summary, Assertion (A) correctly describes the localized nature of DNA replication at the replication fork, and Reason (R) accurately points out that both DNA unwinding and DNA polymerization during replication are energy-dependent processes.