Final answer:
During DNA replication, hydrogen bonds between pairs of nitrogenous bases are broken to allow the DNA double helix to unwind and each strand to act as a template for a new strand.
Step-by-step explanation:
During DNA replication, the correct event that occurs is B) The hydrogen bonds between pairs of nitrogenous bases are broken. This process is essential for the unwinding of the two strands of the DNA double helix, allowing each strand to serve as a template for the synthesis of a new complementary strand. The nucleotides in a DNA molecule are connected to each other in the backbone via phosphodiester bonds, which remain intact during replication. Therefore, answers A, C, and D are incorrect as covalent bonds between nitrogenous bases do not exist, nor are the covalent bonds between sugar and phosphate molecules broken during the process of DNA replication.