Which event marks the beginning of DNA replication?

A) Formation of replication bubble

B) Unwinding of DNA helix

C) Formation of replication fork

B is the correct answer. The beginning of DNA replication occurs with the unwinding of the DNA helix by a special enzyme. The two strands that form the helix then create a replication fork. The two strands are then oriented differently, one becoming the 'leading strand' and one the 'lagging strand'.